If you are going to design a secure method from the scratch, it depends on the way of fulfilling this communication. For example, if you invoke requests using HTTP GET, then SSL connection can be considered as a solution.
Insofar as Trust is not a message, but an outcome, it is recommended to reinforce the fundamental bases of trust, namely Trustworthiness (=the perception of reliability). The three main components of Trustworthiness are competence, benevolence and honesty. Your communication should point out (signal) to your targets these elements. You may use relational signalling theory (RST).
I suggest for example: Six, F. E. (2007). Building interpersonal trust within organizations: a relational signalling perspective. Journal of Management & Governance, 11(3), 285-309.
The different cloud service provider uses the different cloud security services and claim for best security, but there is no mechanism to map the robustness of implementing security. There is a sevrttel security issue between the consumer and provider. You should find the specific security issue and resolve it with different testing phase. You can read this book and paper
Krutz, R. L., & Vines, R. D. (2010). Cloud security: A comprehensive guide to secure cloud computing. Wiley Publishing.
Yu, S., Wang, C., Ren, K., & Lou, W. (2010, March). Achieving secure, scalable, and fine-grained data access control in cloud computing. In Infocom, 2010 proceedings IEEE (pp. 1-9). Ieee.