# Decentralized Storage with Access Control and Data Persistence for e-Book Stores
## 4 Proposed System
### Decentralized Access Control to the Stored Data
#### 4.2.1 Access Control Contract (ACC)
If a public blockchain such as Ethereum is used to implement the proposed method, the history of books purchased by users through their Ethereum accounts can be read by anyone. A possible approach to addressing this problem is to utilize self-sovereign identity (SSI), a system that allows individuals to manage their own identity information and share it securely as needed. This could allow users to have strict control over their own identity information, purchase history, and other data [37]. \begin{table}
\begin{tabular}{l c} \hline \hline
**Function** & **Execution Cost (USD)** \\ \hline claim & 5.09 \\ \hline disclosure & 6.03 \\ \hline leaveNode & 2.62 \\ \hline \hline \multicolumn{2}{l}{mint} & 8.49 \\ \hline register & 7.63 \\ \hline registerNode & 10.21 \\ \hline vote & 4.45 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Estimated gas fees for ACC contract functions at 26 Gwei/gas, 2151.72 USD/ETH. ## 7 Concluding Remarks

In this paper, we propose and evaluate a decentralized architecture for realizing persistent e-book services. The proposed system consists of a smart contract called ACC to control access rights and a d-book-repository to store e-book data in a distributed and persistent manner. Similar to existing decentralized storage systems, the d-book-repository applies Reed-Solomon codes to e-book data to generate \(k\) redundant shards, but unlike existing systems, the set of storage nodes is explicitly partitioned into \(k\) groups, and each shard is uniformly copied to all nodes in one node group. The persistence of the stored e-book data is achieved by the fact that nodes within a node group continue to maintain copies of all shards corresponding to that group, and access rights control is achieved by having each storage node verify the access rights of the downloaders. We built a prototype of the proposed system on AWS and evaluated its performance in various settings. As a result, we confirmed that uploading and downloading a 100 MB file can be completed within 10 s in an environment with low network latency and that the costs required for access control and persistence of stored data are sufficiently small. The proposed method can solve the problem of the inaccessibility of purchased e-books due to reasons such as service termination or intentional data removal by the publisher. However, several issues remain to be addressed, including the enlargement of storage capacity, enhancement of access control functions, and countermeasures against illegal content and unauthorized uploads. Conceptualization, K.O. and S.F. ; methodology, K.O. and S.F. ; software, K.O. ; validation, K.O. ; writing--original draft preparation, K.O. ; writing--review and editing, S.F. and K.O. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Data are contained within the article. The authors declare no conflict of interest. ## References

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