# Comprehensive Review of Storage Optimization Techniques in Blockchain Systems
## 4 Methods
### Data Deduplication
Additionally, to ensure the security of the deduplication process and the reliability of key management, BDKM adopts a secret sharing technique that splits the encryption key into multiple key fragments stored across a distributed blockchain network. Each key fragment is stored as part of a blockchain transaction, leveraging the immutability and distributed consensus mechanisms of blockchain to prevent single points of failure and mitigate potential key leakage risks. By integrating deduplication technology with blockchain, the BDKM scheme not only achieves significant storage space savings but also provides a highly secure and reliable cloud storage solution. [PERSON] et al. [93] introduced an advanced deduplication scheme, termed ESDedup (Efficient and Secure Deduplication), designed to address data redundancy challenges in blockchain storage. This scheme incorporates data similarity computation to detect and eliminate highly redundant data blocks, thereby ensuring the retention of only unique instances in storage. For data blocks with high similarity, the system manages access rights for multiple users through a reference mechanism, obviating the need for redundant data replication. To maintain security and transparency during deduplication, ESDedup records the hash values of data blocks and associated access permissions on the blockchain. The inherent immutability of blockchain technology is utilized to safeguard data integrity and security. Moreover, the scheme incorporates a smart contract-based auditing strategy, which automates the management and verification of deduplication processes. This approach reduces storage costs traditionally incurred during auditing and significantly enhances storage resource utilization efficiency. Experimental results demonstrate that, compared to leading existing methods, ESDedup improves system scalability and performance, achieving a 55.9% increase in deduplication rate. [PERSON] et al. [94] proposed a scheme aimed at reducing data redundancy in blockchain storage through secure data deduplication. The approach is implemented as follows: first, by integrating Message-Locked Encryption (MLE) technology, identical data produces the same ciphertext during encryption, enabling the system to detect and eliminate duplicate ciphertexts upon data upload. As a result, only a unique encrypted output is stored, which avoids redundant storage of identical data copies. Second, the authors enhanced the authenticator generation algorithms, allowing the deduplication of authenticators in scenarios where multiple users share the same data. This enables the system to store a single authenticator to verify access rights for multiple users. By integrating these two techniques, the proposed scheme significantly reduces data redundancy in blockchain storage while ensuring data security and integrity, thereby optimizing the utilization of storage resources. Table 5 demonstrates the effectiveness of using data deduplication techniques to reduce storage redundancy in blockchain systems. It lists the applied approaches and their storage efficiency.