Cloud Computing has been envisioned as the next generation architecture of IT Enterprise. The Cloud computing concept offers dynamically scalable resources provisioned as a service over the Internet. Economic benefits are the main driver for the Cloud, since it promises the reduction of capital expenditure and operational expenditure. In order for this to become reality, however, there are still some challenges to be solved. Most important among these are security and trust issues,since the users data has to be released to the Cloud and thus leaves the protection sphere of the data owner.In contrast to traditional solutions, where the IT services are under proper physical,logical and personnel controls, Cloud Computing moves the application software and databases to the large data centers, where the management of the data and services may not be fully trustworthy.