Security Analysis and Improvement of a Dynamic-Hash-Table Based Auditing Scheme for Cloud Storage

Cloud storage has emerged as a promising solution to the scalability problem of massive data management for both individuals and organizations, but it still faces some serious limitations in reliability and security. Recently, Tian et al. proposed a novel public auditing scheme for cloud storage (DHT-PA) based on dynamic hash table (DHT), with which their scheme achieves higher efficiency in dynamic auditing than the state-of-the-art schemes. They claimed that their scheme is provably secure against forging data signatures under the CDH assumption. Unfortunately, by presenting a concrete attack, we demonstrate that their scheme is vulnerable to the signature forgery attack, i.e., the cloud service provider (CSP) can forge a valid signature of an arbitrary data block. Thus, a malicious cloud service provider can pass the audit without correct data storage. The cryptanalysis shows that DHT-PA is not secure for public data verification. The purposed of our work is to help cryptographers and engineers design/implement more secure and efficient identity-based public auditing schemes for cloud storage by avoiding such kind of attacks.