Cloud computing is a growing paradigm with tremendous momentum. It offers on-demand use of third party IT infrastructures on a pay-per-use basis. This paradigm reduces customers' need for hardware while improving the elasticity of computational resources, allowing them to adapt to business requirements. But its unique features exacerbate security and privacy issues and became challenges. Current research on cloud security is still in the early stages and no universal model or set of techniques, which can provide full proof solution to it, has yet emerged.