Grid computing is a newly developed technology for complex systems with large-scale resource sharing and multi-institutional collaboration. The prominent feature of grid computing is the collaboration of multiple entities to perform collaborative tasks that rely on two fundamental functions: communication and resource sharing. Since the Internet is not security-oriented by design, there exist various attacks, in particular malicious internal and external users. Securing grid communication and controlling access to shared resources in a fine-tuned manner are important issues for grid services. This paper proposes an elegant Dual-Level Key Management (DLKM) mechanism using an innovative concept/construction of Access Control Polynomial (ACP) and one-way functions. The first level provides a flexible and secure group communication technology while the second level offers hierarchical access control. Complexity analysis and Simulation demonstrate the efficiency and effectiveness of th...