Increasing usage of hardware and software infrastructures has led to notable development of cloud computing technology. By emerging users’ new requirements and variety of organization’s IT services, a single cloud provider (CP) is not capable of serving all users growing requests. To overcome limitations of the current cloud computing structure, cooperation of cloud providers and sharing their infrastructures in the form of cloud federations has been introduced as a promising and interesting solution. Therefore, designing appropriate architecture and framework for cooperation of CPs is inevitable. Trust of CPs to each other’s and selecting suitable cooperator is one of challenging issues to cloud federation realization. In this regard, forming the stable coalitions in the form of trusted cloud federations by using of the cooperative game theory is the main focus of this thesis. Based on the proposed method of this research, CPs are capable of analyzing their cooperators and refuse to cooperate with malicious CP. To compute the trust of CPs to each other, a dynamic trust function composed of direct and indirect trust is proposed. In modeling of indirect trust, for preventing CPs from sending incorrect recommendations, credibility update function has been improved. Moreover, QoS factors of cloud services are considered in the computation of the trust function. In addition, the proposed trust function is applied as a payoff function to a dynamic and distributed coalition formation hedonic game. In the proposed algorithm, each CP is required to get the approval of the CPs members of the selected coalition to join. This property causes, remarkably, reduction of the number of malicious CPs in the final coalition structure and isolates the malicious CPs in singleton coalitions. Convergence and stability of the coalition formation game are analyzed and proved. Furthermore, simulation of proposed algorithm is presented for twenty cloud service providers with random initial conditions. The results shows the homogeneity up to 95% of the coalitions after six time slots and also appropriate time response and availability of cloud federations. Key Words: Cloud Computing, Cloud Federation, Trust, Game Theory, Coalition Formation Games
