# Comprehensive Review of Storage Optimization Techniques in Blockchain Systems
## 5 Summary and Future Directions
### Summary
#### 5.1.1 Security  
Security is one of the challenges faced in blockchain systems. This section provides a comprehensive analysis of various solutions proposed in the paper. * Pruning Technique In optimizing blockchain storage, pruning techniques, while effective in reducing storage requirements and accelerating node synchronization, can also introduce a series of security risks. Firstly, deleting historical blocks may compromise data integrity and the immutability of transactions, rendering nodes unable to verify the complete transaction history. Secondly, if only a few nodes retain the full blockchain data, the level of decentralization is reduced, increasing the risk of network dominance by a minority of controlling nodes. Additionally, the lack of historical data could impact the accuracy of transaction verification, raising the potential for fraud and malicious attacks. Pruning strategies may also affect the normal operation of smart contracts, particularly for applications dependent on historical data, potentially leading to logical and functional failures. Moreover, in industries such as finance and healthcare, which have strict data storage requirements, pruning techniques may present challenges for compliance and auditing. Thus, balancing storage optimization with security necessitates exploring more advanced pruning strategies to ensure that storage efficiency improvements do not compromise the security and data resilience of the blockchain. * IPFS Optimization Introducing the IPFS system for blockchain storage optimization can effectively reduce storage demands but also bring a series of security challenges. Data availability relies on the selection of IPFS network nodes, and when nodes go offline or decide not to store blockchain data, other nodes may be unable to locate or access these data, potentially leading to inaccessible or permanently lost data. IPFS lacks built-in privacy protection and access control mechanisms, making it susceptible to the exposure of sensitive information. As an open system, all data within IPFS can be publicly accessed via content hashes; thus, once a hash value is publicly disclosed, anyone can retrieve the stored content. The IPFS system is also vulnerable to DDoS attacks and lacks an incentive mechanism to ensure long-term data storage and availability. Therefore, these security issues must be carefully evaluated when adopting IPFS. * Data Sharding In a sharded architecture, each node stores only a portion of the data, so if a node fails or is attacked, the shard data may become lost or unavailable. In cross-shard transactions, where data transfer and verification are required between multiple shards, the complexity of operations and potential latency are increased. Additionally, in the blockchain consensus mechanism, if each shard employs a different consensus mechanism, achieving consistent global consensus across all shards becomes a significant challenge. Improper consensus mechanism settings could pose risks to the overall blockchain system. * Erasure Code Optimization Erasure coding requires close cooperation among nodes to distribute, encode, store, and recover data, which adds complexity to system design. In a decentralized blockchain system, ensuring that all nodes correctly execute the erasure coding protocol and provide the required data blocks for data recovery poses a challenge. Erasure coding primarily addresses fault tolerance for data loss but has limited capability for detecting data tampering. If malicious nodes alter some data blocks and other nodes cannot promptly detect these tampering actions, incorrect data may propagate within the blockchain system, undermining both system consistency and integrity. * Deduplication Deduplication reduces storage requirements by eliminating redundant data blocks, meaning that identical data blocks are stored only once. If a data block is maliciously modified, all transactions or records referencing that block will be affected, leading to data integrity issues.