# Secure and Efficient Deduplication for Cloud Storage with Dynamic Ownership Management
## 7 Conclusions  
This paper proposes an efficient and secure data deduplication protocol based on the secure data sharing in cloud (SeDaSC) protocol. Our proposal addresses three key aspects of SeDaSC. First, our approach enhances data privacy. In SeDaSC, the cryptographic server (CS) performs complex encryption operations on the behalf of clients, potentially compromising data privacy as the CS can access plaintext. Our approach mitigates this concern by having clients perform blind encryption using hash values of plaintext, thus preventing information exposure. Second, our approach enhances the efficient utilization of cloud storage space. SeDaSC introduced a data-sharing method using cloud storage. However, it lacks an effective method for storage space management. Data deduplication technology stands out as an efficient approach to managing data, involving the prevention of storing data twice in cloud storage if they are already uploaded. This technique has \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{2}{c}{**SeDaSC Protocol**} & \multicolumn{2}{c}{**Our Protocol**} \\ \cline{3-6}  & & \multicolumn{2}{c}{**Computational**} & \multicolumn{2}{c}{**Communication**} & \multicolumn{2}{c}{**Computational**} & \multicolumn{2}{c}{**Communication**} \\  & & **Overhead** & **Overhead** & **Overhead** & **Overhead** \\ \hline \multirow{3}{*}{Upload} & Client & 0 & \(\lambda_{P}\) & \(2H+2\bigoplus\) & \(\lambda_{H}\) \\  & CS & RBG + \(1H+1\bigoplus+1\)SE & \(\lambda_{K}+\lambda_{C}\) & RBG + \(1\)SE & \(\lambda_{C}\) \\  & Cloud storage & 0 & 0 & RBG + \(1\)SE + \(4\bigoplus\) & \(2\lambda_{K}\) \\ \hline \multirow{3}{*}{Download} & Client & 0 & \(\lambda_{K}\) & 0 & \(\lambda_{H}\) \\  & CS & 1 SD & \(\lambda_{P}\) & 1 SD & \(\lambda_{H}+\lambda_{C}\) \\  & Cloud storage & 0 & \(\lambda_{C}\) & 1 SD & \(\lambda_{C}\) \\ \hline \multirow{3}{*}{Ownership update} & Client & - & - & \(1\bigoplus\) & 0 \\  & CS & - & - & \(N_{C}\times\bigoplus\) & \(N_{C}\times\lambda_{K}\) \\ \cline{1-1}  & Cloud storage & - & - & RBG + \(1\)SE + \(4\bigoplus\) & \(2\lambda_{K}\) \\ \hline \hline \end{tabular} \(H\): hash function; \(\bigoplus\): XOR operation; RBG: random bit generation; SE: symmetric key encryption; SD: symmetric key decryption; \(\lambda_{P}\): the size of plaintext; \(\lambda_{H}\): the output size of hash function; \(\lambda_{C}\): the size of ciphertext; \(\lambda_{K}\): the size of secret key; \(N_{C}\): the number of clients in group.  
\end{table} 
Table 4: Comparison of overheads between the SeDaSC protocol and our protocol. the potential to save storage space by up to 90% [3]. Our proposed protocol enables data deduplication based on client ownership stored in an access control list (\(ACL\)), thereby ensuring efficient use of cloud storage space. Third, our approach ensures the secure management of data, including dynamic ownership management, when the composition of a group changes. SeDaSC does not consider specific scenarios related to the addition, modification, or deletion of client ownership, which may lead to security issues. While SeDaSC only allows access to stored data by clients with legitimate ownership, it does not address scenarios involving ownership changes. For instance, security issues might arise when newly registered clients are granted access to previous data or when revoked ownership clients continue to access data stored in cloud storage. Our proposed protocol addresses these concerns by allowing for the registration or deletion of ownership and distributing refreshed group keys for the respective session to prevent both previous and new clients from accessing ciphertext. The SeDaSC protocol requires only one hash function operation, thereby providing advantages in terms of client computation cost and time during data uploads. However, this approach may pose data privacy concerns as it exposes plaintext to the CS. Our protocol addresses this issue by conducting one hash function and one XOR operation.