# Secure and Efficient Deduplication for Cloud Storage with Dynamic Ownership Management
## 2 Related Work
### Server-Side Deduplication
As a result, the email server stores unique emails and links duplicate emails through pointers. In 2017, [PERSON] et al. proposed a data deduplication protocol based on decentralized server-aided encryption with multiple key servers [13]. Server-aided encryption refers to the help of a server when a client wants to retrieve data. In this context, the server referred to here is a key server. When a client sends a query, the key server encrypts this query before sending it to the cloud. Importantly, the key server does not understand the client's query, ensuring confidentiality even in a multi-user environment. The proposed protocol does not involve secret key sharingamong key servers and is a decentralized architecture, making it scalable and suitable for widespread deduplication across various key servers. In 2020, [PERSON] et al. presented a blockchain-based public auditing protocol that allows for automatic penalties against malicious cloud service providers (CSPs) [14]. The proposed protocol offers compensation to clients when their data integrity is compromised and provides a means to penalize malicious CSPs. To ensure secure and consistent data encryption, the protocol uses MLE [9] with hash and CE with tag check. In this way, various methods employing server-side deduplication have been proposed to address different scenarios. Some of these studies have focused on scenarios involving a large number of clients or substantial data storage requirements. In 2016, [PERSON] et al. proposed a secure server-side deduplication that remains secure even in environments where the ownership of outsourced data changes frequently [6]. In practical scenarios, when providing cloud storage services, changes in data ownership are likely to occur frequently. For example, a client who previously owned data but had their ownership revoked should no longer have access to data stored in cloud storage. The proposed protocol updates the encryption key each time ownership for data changes, satisfying both forward and backward secrecy. Additionally, the updated encryption keys are selectively distributed to valid owners, and the method strictly manages data access by the owners. In 2021, [PERSON] et al. proposed a data deduplication protocol for secure data sharing [7] based on a deduplication method for authenticated clients [4]. In this proposed approach, the cryptographic server (CS) generates the CE key on behalf of the client and sends it to the client. The client encrypts the plaintext using the encryption key received from the CS and sends it back to the CS. The CS accesses an access control list (\(ACL\)) to confirm data duplication and decide on storage eligibility. This protocol successfully addresses privacy issues [4] but has the limitation of increasing the computational load on the client during this process. Therefore, it appears that there are no existing papers that address the changing environment efficiently and securely, as proposed in this paper. In 2022, [PERSON] et al. introduced a novel server-side deduplication scheme for encrypted data employing hybrid clouds [15]. This approach involves storing data in the public cloud while ownership information and hash code sets for data are stored in the private cloud.