Cloud computing is a whole new paradigm that offers a non-traditional computing model for organizations to adopt Information Technology and related functions and aspects without upfront investment and with lower Total Cost of Ownership (TCO). Cloud computing opens doors to multiple, unlimited venues from elastic computing to on demand provisioning to dynamic storage and computing requirement fulfillment. However, despite the potential gains achieved from the cloud computing, the security of an open-ended and rather freely accessible resource is still questionable which impacts the cloud adoption. The security problem becomes amplified under the cloud model as new dimensions enter into the problem scope related to the architecture, multi-tenancy, layer dependency, and elasticity. This paper introduces a detailed analysis of the cloud security problem. It investigates the problem of security from the cloud architecture perspective, the cloud characteristics perspective, cloud delivery model perspective, and the cloud stakeholder perspective. The paper investigates some of the key research challenges of implementing cloud-aware security solutions which can plausibly secure the ever-changing and dynamic cloud model. Based on this analysis it presents a derived detailed specification of the cloud security problem and key features that should be covered by any proposed security solution for cloud computing.