# A Searchable Encryption with Forward/Backward Security and Constant Storage
## 4 Our Proposed Algorithm
### Decryption
In terms of storage overhead, in order to reduce the occupation of local storage resources, the design of iteratively nested hash functions is used to ensure that the size of each node is consistent, and that constant storage overhead is maintained without increasing the length of the keyword index chain. The above structure creates a large number of hash operations, and the experimental analysis shows that the hash function generates negligible efficiency to the operation of the algorithm. In comparison with similar schemes, our scheme still has some advantages in terms of computational overhead. As a result, we achieve constant storage overhead and high encryption and decryption efficiency. Future research work should explore improvements in function, time cost, and safety on the basis of this scheme. These results prove that our scheme can be applied to a wider range of applications, such as low-performance computers. ## 7 Conclusions

In this article, we analyze the problems of the related dynamic searchable encryption schemes and the solutions proposed by different scholars according to various aspects. We proposed a dynamic searchable encryption scheme with constant storage, which adopts a double-layer structure and iteratively uses hash functions. The scheme satisfies forward and backward security, while also achieving low computational overhead. The experimental evaluation shows the superiority of our scheme relative to the current mainstream algorithms. Our proposed scheme can be applied to a small encryption environment to provide privacy protection, i.e., the internal network of a company or scientific research institution, where the ciphertext is stored centrally to ensure that unauthorized users cannot have access. At present, our research has not implemented a multi-keyword search. In future work, we will consider including a multi-keyword search to improve accuracy and protect user search patterns vs. access patterns. \begin{table}
\begin{tabular}{c c c c} \hline
**Dataset** & **Number of Files** & **Number of Keywords** & **Keyword/Document Pairs** \\ \hline Dataset 1 & 2000 & 7563 & 55,323 \\ Dataset 2 & 5000 & 12,315 & 263,597 \\ Dataset 3 & 10,000 & 29,681 & 438,762 \\ \hline \end{tabular}
\end{table} 
Table 4: Test data table. \begin{table}
\begin{tabular}{c c c c} \hline
**Scheme** & **Dataset 1** & **Dataset 2** & **Dataset 3** \\ \hline
[21] & 3842 kb & 7613 kb & 8922 kb \\
[16] & 1974 kb & 4012 kb & 6474 kb \\
[18] & 3963 kb & 5563 kb & 10,072 kb \\ Ours & 843 kb & 843 kb & 843 kb \\ \hline \end{tabular}
\end{table} 
Table 5: Performance of each scheme under the effect of different databases. **Author Contributions:** Conceptualization, S.C. and J.Y. ; methodology, J.Y. ; software, J.Y. ; validation, J.Y. and Z.F. ; formal analysis, J.Y. ; investigation, S.C.; resources, J.Y. ; data curation, J.Y. ; writing--original draft preparation, J.Y. ; writing--review and editing, S.C.; visualization, Z.F. ; supervision, C.W. ; project administration, S.C. and J.Y. ; funding acquisition, J.Y. and S.C. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the National Natural Science Foundation of China (No. 62262060) and the Industrial Support Plan Project of the Gansu Provincial Department of Education (2022 CYZC-17). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable. **Conflicts of Interest:** The authors declare no conflict of interest. ## References

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