Efficient key management for enforcing access control in outsourced scenarios

Data outsourcing is emerging today as a successful paradigm allowing individuals and organizations to exploit external servers for storing and distributing data. While trusted to properly manage the data, external servers are often not authorized to read them, therefore requiring data to be encrypted. In such a context, the application of an access control policy requires different data to be encrypted with different keys so to allow the external server to directly enforce access control and support selective dissemination and access. The problem therefore emerges of designing solutions for the efficient management of the encryption policy enforcing access control, with the goal of minimizing the number of keys to be maintained by the system and distributed to users. Since such a problem is NP-hard, we propose a heuristic approach to its solution based on a key derivation graph exploiting the relationships among user groups. We experimentally evaluate the performance of our heuristic solution, comparing it with previous approaches.