Cloud computing is a new paradigm which enables users to reduce their costs and is advantageous to both the serving and served organizations. However, security issue is a major concern in the adoption of cloud computing. The most effective way of protecting cloud computing services, resources and users is access control. This paper intends to provide a trust-based access control mechanism for cloud computing considering its multi-domain aspects. Firstly, trust is introduced into cloud computing environment and trust relationships between users and cloud platform are built. It also analyzes the difference between intra-domain trust and inter-domain trust. Furthermore, a role-based access control framework combined with trust degree in multi-domain is given from this paper. Access control in local domain directly applies RBAC model combined with trust degree, whereas in multi-domain it contains the conception of role translation. The simulation results show that the proposed method is more suitable to cloud environment and definitely can improve the reliability and validity of the system.

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Considering trust issues in cloud computing, we analyze the feasibility of adopting ant colony optimization algorithm to simulate trust relationships between entities in the cloud and then propose a novel behavior trust model: ACO-BTM. Trust relationships between entities in cloud computing are dynamic, uncertain and hard to quantify. ACO-BTM introduces the conception of 'pheromone' and transition probability to represent behavior trust. Then, it focuses on the research of dynamic trust evaluation, time constraint and some other issues. Furthermore, a detailed algorithm process of behavior trust evaluation is given in this context. Finally, ACO-BTM is applied to cloud computing platform to simulate the establishment of behavior trust relationships. The simulation experiment verifies that trust degree change with time varies and the frequency of interactions. Compared with the other model, ACO-BTM can provide better trust recommendation services and protect against attacks of malicious nodes effectively in cloud computing environment. It is proved that ACO-BTM has good flexibility, accuracy and robustness.