# Lightweight, Secure, Similar-Document Retrieval over Encrypted Data
## 4 Scheme Overview
### Private Similarity Computation and Search Queries Stage
The consuming time for query generation was estimated for this work, as well as the EsPRESSo and GBF protocols for sets of different sizes. Figure 15 shows that EsPRESSo is comparable to this protocol. This is because the EsPRESSo protocol applies the Min-Hash technique, which incurs significantly lower computation overheads; while this paper's scheme applies the Winnowing algorithm on the hash values set as a filtering mechanism to select only the fundamental property. Thus, the consuming time of the query generation is highly sensitive to the number of hash values. Moreover, the slight difference in computational overheads occurred as a result of stronger security claims for query generation in the proposed protocol's security requirement. In any case, this difference is considered simple and does not have a tangible effect during implementation by the client, thus enabling the conclusion that EsPRESSo and the present study's method can each be applied with lightweight client implementation. It should also be noted that this paper's method has a higher performance in terms of document scalability and document retrieval accuracy, as shown previously. For query generation time, the GBF method has lower performance, indicating that it cannot be used in devices with limited resources. Recall at GBF required 2 \(\searrow\) public key operations in the client side for each Naor-Pinkas OT operation in order to meet the stronger privacy claims in the GBF proposal. Figure 14: Performance of private and secure DSD (5000 \(\times\) 5000 documents). ## 8 Conclusions

There is a real need for a methodical and functional method of retrieving and ranking private similar documents, especially in large text libraries. This work has tackled the issue of preserving privacy while detecting document similarity as well as retrieving and ranking these documents over encrypted data. In other words, the importance of the proposed work stems from its ability to compare encrypted documents in a way that reduces complexity while preserving privacy. The Winnowing algorithm was employed in this method to select the most important and effective fingerprint for each document in an efficient manner, which led to low space complexity and low response times for the client. Fingerprints were compressed versions of \(k\)-gram sets, capable of detecting both full and partial copies. Thus, an inverted index was developed based on the fingerprint set, permitting accurate, efficient, fast identification of matching documents, which is a greatly simplified process that results in low response times on the client side. This was then secured by utilizing a Paillier homomorphic encryption system. This cryptosystem allows the posting vectors to be summed without decryption. In order to demonstrate the functional benefits of this methodology, a number of experiments were conducted. These experiments prove that this method is more efficient than other major methods of privacy-preserving, secure, and similar document retrieval over encrypted data for lightweight client implementation with resource-limited devices. In addition, the linear computational complexity of our proposed work remains stable with the increase in the size of document sets. However, the communication cost of the proposed method is a limiting factor. Future research will focus on developing this system to include the capability to detect plagiarism and distinguish inherent plagiarism without a reference corpus. There is also scope to improve the proposed system by attaching further functions to the service, as well as by utilizing cluster-based inverted indexing and parallel programming to lessen the runtime. Furthermore, the possibility exists to refine the methodology with an additional stage which will retrieve a text from the gathered group which is more similar to the document being queried. The addition of this measure might be proven to be influential in the overall performance of the proposed procedure.