Abstract: With the successful development of cloud computing business models, three major cloud computing service models have been formed: Platform as a service, software as a service and infrastructure as a service. The traditional industry providers eagerly moved to join the cloud computing research, but the intense competitions make it difficult to standardize the cloud computing and to realize the interoperability and cross-platform migration. Meanwhile, the numerous cloud platforms result in that users do not know how to make their choice due to the different cloud platforms without a unified, credible evaluation criteria. In this paper, first, a detailed analysis of various scenarios on the demand for cross-platform services is given, which shows the necessity and inevitability of building a “cross-platform as a service” model. Second, by using the trusted third party to achieve this cross-platform as a service. We give the standard process of data exchange and migration in the cross-platform under the supervision of the trusted third party, and provide users with a credible third-party-centered cloud platform evaluation criterion of security and credibility. This will provide the valuable suggestions for enterprise to choose proper cloud platform services.

Key words: cloud computing；trusted third party, trust value, security value, cross platform as a service