The use of cloud computing has revolutionized the way in which cyber infrastructure is used and managed. The on-demand access to seemingly infinite resources provided by this paradigm has enabled technical innovation and indeed innovative business models and practices. This rosy picture is threatened, however, by increasing nefarious interest in cloud platforms. Specifically, the shared tenant, shared resource nature of cloud platforms, as well as the natural accrual of valuable information in cloud platforms, provide both the incentive and the possible means of exploitation. To address these concerns we are developing a self-defending, self-evolving, and self-accounting trustworthy cloud platform, the TCloud. Our approach in realizing TCloud holds to the following five tenets. First, defense-in-depth through innate containment, separation and diversification at the architectural level. Second, least authority by clear separation of functionality and associated privilege within the architecture. Third, explicit orchestration of security functions based on cloud-derived and external intelligence. Fourth, moving-target-defense through deception and dynamic evolution of the platform. Fifth, verifiable accountability through light weight validation and auditable monitoring, record keeping and analysis. Our approach to fundamentally refactor the cloud architecture to explicitly enable security related functionality lays the foundation for truly trustworthy cloud computing. Given the unrelenting push towards the use of cloud technologies our work has broad applicability across industry, healthcare, government and academia. All software we develop will be released to the community in open source form.