Abstract: Aiming at the problems of data confidentiality and user’s privacy leakage in cloud， this paper proposes an efficient and secure cloud storage scheme with hidden access patterns. Firstly， the files are divided into data blocks with fixed sizes， and encrypted by pseudo-random functions and collision-resistant Hash functions. Then， in order to construct the secure cloud storage structure， the blocks are uploaded into pseudo-random collection superset in the cloud server. Meanwhile， a two-round access strategy that hides the access patterns， reduces the storage cost and access interaction is designed. Security analysis shows that the proposed scheme achieves L₁L₂-dynamic adaptive security. Experimental results show that the proposed scheme can not only protect data confidentiality， but also be more suitable for the actual cloud storage.

Key words: cloud storage, access pattern, pseudo-random function, collision-resistant Hash function, confidentiality