ABSTRACT Cloud computing, an emerging field in Information technology has changed the perception of infrastructure architectures, software delivery and deployment models. The concept of Cloud computing comes into focus when the basic aspect of information technology is considered which involves a way to increase capacity on the fly without much investment either in hardware or software. In a nutshell, cloud computing could be classified as a term for delivering hosted services, dynamically scalable and shared resources on the internet. Research in this technology has gained tremendous momentum in the past few years since its inception and one of the key research areas is considered to be the security aspects of cloud computing. This paper will classify the three models of cloud computing, some key differentiating aspects between cloud, grid and distributed computing, a comprehensive study on the major security concerns in cloud computing, its mitigation and describe a secure cloud computing framework with an implementation of Single Sign on mechanism on Ubuntu Enterprise Cloud