# 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)
Considering that the price of a Kindle book is around USD 4 to 15, this result means that deploying the service on Ethereum will be a big burden for e-book users. Since the execution cost on other blockchains is proportional to the transaction fee (avg) shown in Table 7, the execution cost on those blockchains is not a big issue. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**\# of e-Books** & **10,000** & **100,000** & **200,000** \\ \hline t2.micro & 4128.06 ms & 39,196.68 ms & 90,958.94 ms \\ m5.xlarge & 74.59 ms & 1804.42 ms & 24,736.23 ms \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Time taken for generating an answer to the quiz. \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Blockchain** & **Max Recorded TPS**[34] & **Current TPS**[34] & **Block Time**[34] & **Transaction Fee (Avg)**[35] \\ \hline Ethereum & 57.91 tx/s & 10.98 tx/s & 12.24 s & 1.30 USD \\ Polygon & 273 tx/s & 57.05 tx/s & 2.44 s & 0.00061 USD \\ Arbitrum & 175 tx/s & 15.56 tx/s & 0.25 s & 0.0046 USD \\ Solana & 2712 tx/s & 447 tx/s & 0.42 s & 0.00032 USD \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of performance metrics across major blockchains. ## 6 Discussion

This section discusses several points to be noted in the practical application of the d-book-repository. The first issue concerns the storage capacity limit. The d-book-repository is designed to store shards generated from contents on all storage nodes in a uniform manner. Therefore, as long as the storage capacity provided by each node is fixed, the total capacity does not increase with the number of nodes, as in many other distributed storage systems. For example, assuming that each node provides 1 TB of storage and that each content item is encoded in 20 shards, the system can store up to 20 TB of content no matter how many nodes are added. This amount is equivalent to 200,000 e-books of 100 MB, which seems to be sufficiently large at the present time. However, since the amount of stored content grows monotonically, it is likely to eventually be used up over time. The easiest way to solve this problem is to keep replacing the storage devices of each node in the system with larger capacity ones as the underlying device technology advances, but this imposes the burden of updating on the storage node provider, thus compromising sustainability. One solution to overcome this issue is to increase the capacity of all nodes' contributions after reaching an agreement among all storage nodes. If less than half of the storage nodes do not comply with the agreement, they will not be able to answer the incentive quiz correctly and will not receive a reward, thus the result of the agreement will be binding. The second issue is how to prevent unauthorized downloads. There may be rogue nodes on the network that fail to verify the downloader's access rights, and users of the proposed system can restore the entire content regardless of the existence of access rights if they find the required number of rogue nodes belonging to different groups. Potential solutions to this issue encompass penalizing nodes that fail to verify access rights or utilizing encryption in conjunction with content protection measures. The third issue is countermeasures against uploading illegal contents and unauthorized registration by non-copyright holders [36]. Once illegal content is uploaded to the network, it is difficult to completely remove it, and it is also difficult to verify with certainty whether the Ethereum address (EOA) used for content registration belongs to the copyright holder. Similar problems have been noted with other distributed storage systems. For example, Arweave claims to employ a blacklist to prevent the spread of illegal content, but the effectiveness of this approach is questionable. Presently, the most efficacious preemptive measure against such threats appears to involve pre-upload screening by a trusted third party. The fourth issue is the protection of user privacy.