On protecting integrity and confidentiality of cryptographic file system for outsourced storage

Abstract

A cryptographic network file system has to guarantee confidentiality and integrity of its files, and also it has to support random access. For this purpose, existing designs mainly rely on(often ad-hoc) combination of Merkle hash tree with a block cipher mode of encryption. In this paper, we propose a new design based on a MAC tree construction which uses a universal-hash based stateful MAC. This new design enables standard model security proof and also better performance compared with Merkle hash tree. We formally define the security notions for file encryption and prove that our scheme provides both confidentiality and integrity. We implement our scheme in coreFS, a user-level network file system, and evaluate the performance in comparison with the standard design. Experimental results confirm that our construction provides integrity protection at a smaller cost.