Improvement of a Remote Data Possession Checking Protocol from Algebraic Signatures

Cloud storage allows cloud users to enjoy the on-demand and high quality data storage services without the burden of local data storage and maintenance. However, the cloud servers are not necessarily fully trusted. As a consequence, whether the data stored on the cloud are intact becomes a major concern. To solve this challenging problem, recently, Chen proposed a remote data possession checking (RDPC) protocol using algebraic signatures. It achieves many desirable features such as high efficiency, small challenges and responses, non-block verification. In this paper, we find that the protocol is vulnerable to replay attack and deletion attack launched by a dishonest server. Specifically, the server can either fool the user to believe that the data is well maintained but actually only a proof of the challenge is stored, or can generate a valid response in the integrity checking process after deleting the entire file of the user. We then propose an improved scheme to fix the security flaws of the original protocol without losing the desirable features of the original protocol.