Multi-user dynamic proofs of data possession using trusted hardware

Abstract

In storage outsourcing services, clients store their data on a potentially untrusted server, which has more computational power and storage capacity than the individual clients. In this model, security properties such as integrity, authenticity, and freshness of stored data ought to be provided, while minimizing computational costs at the client, and communication costs between the client and the server. Using trusted computing technology on the server's side, we propose practical constructions in the provable data possession model that provide integrity and freshness in a dynamic, multi-user setting, where groups of users can update their shared files on the remote, untrusted server. Unlike previous solutions based on a single-user, single-device model, we consider a multi-user, multi-device model. Using trusted hardware on the server helps us to eliminate some of the previously known challenges with this model, such as forking and rollback attacks by the server. We logically separate bulk storage and data authentication issues to different untrusted remote services, which can be implemented either on the same or different physical servers. With only minor modifications to existing services, the bulk storage component can be provided by large-scale storage providers such as Google, CloudDrive, DropBox, and a smaller specialized server equipped with a trusted hardware chip can be used for providing data authentication. Our constructions eliminate client-side storage costs (clients do not need to maintain persistent state), and are suitable for situations in which multiple clients work collaboratively on remotely stored, outsourced data.