# A New Blockchain-Based Multi-Level Location Secure Sharing Scheme
## 4 Our Proposed Scheme
### Our Proposed Scheme
#### 4.2.2 Location Record
Compared with the related work BMLPS, the computing cost of our proposed scheme is significantly lower, which is proved by the experimental results in Section 5. ### Flexibility

Our proposed scheme is flexible, which stems from two aspects: (1) In our proposed scheme, \(LP\) freely sets the accuracy of the location information obtained by \(LD\)s with different access levels, which cannot be realized in BMPLS due to using the quad-tree function to partition the region. (2) Access control should be flexible to be adapted to different contexts. In our proposed scheme, \(LP\) can call the smart contract to record policy to flexibly set the access levels of \(LD\)s.

### Acceptable Gas Cost

In our proposed scheme, the gas costs of the smart contract are acceptable, as shown in Section 5.5. However, frequent modifications to the policy of \(LP\) and the public attribute of \(LD\), and \(Fnode\) frequently verifying data and reporting \(LP\), will bring extra-high gas costs. This situation needs to be avoided. In essence, the more stable the public attribute of \(LD\), the better. The addition of new \(LD\)s should also be controlled. ### Performance Comparison

In this section, we compare our proposed scheme with related schemes, including K-anonymity, UB-PPD [32], Medblock [34], and BMPLS [35]. Table 1 shows that our proposed scheme is overall better, where \"\(\surd\)\", \"\(\times\)\" and \"-\" denote satisfied, dissatisfied and uninvolved, respectively. ## 7 Conclusions

In our proposed scheme, we replaced the central database with a blockchain in the location sharing. The decentralization and immutability of the blockchain make our proposed scheme applicable to a system composed of peer nodes without a central server. Protecting user location privacy and verifiable location data is our focus. We use the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Scheme** & **K-Anonymity** & \begin{tabular}{c} **UB-PPD** \\ **[**32**]** \\ \end{tabular} & \begin{tabular}{c} **MedBlock** \\ **[**34**]** \\ \end{tabular} & \begin{tabular}{c} **BMPLS** \\ **[**35**]** \\ \end{tabular} & \begin{tabular}{c} **Our Proposed** \\ **Scheme** \\ \end{tabular} \\ \hline \begin{tabular}{c} Multi-level privacy \\ protection \\ Verifiability \\ \end{tabular} & - & \(\times\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \begin{tabular}{c} Robust \\ Immutability \\ \end{tabular} & \(\times\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \begin{tabular}{c} Confidentiality \\ \end{tabular} & \(\surd\) & \(\times\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \
\begin{tabular}{c} Decentralization \\ Low computing cost \\ \end{tabular} & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\
\begin{tabular}{c} Flexibility \\ Acceptable gas cost \\ \end{tabular} & - & - & - & - & \(\surd\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Performance comparison with related works. multi-level setting of location data and effective access control to realize the former. To this end, we strip the location data into multi-level virtual location data and offset vectors, and design smart contract \(SC\) to implement attribute-based access control. The incentive and punishment mechanism established by \(SC\) can drive users in the network to work honestly. Besides these, we use hash algorithms, Merkle tree and the immutability of blockchain to achieve data verifiability. The results of the experimental evaluation and theoretical analysis show that our proposed scheme is more efficient and secure than the existing works. Smart contracts are not used in related schemes [32; 34; 35]. In our proposed scheme, the smart contract brings extra gas costs. However, we believe that the gas cost is acceptable when the above properties are achieved. An increasing number of resources scattered in the network are willing to provide data storage services, which can be seen from the development of technologies such as BT, PT and IPFS in recent years. This type of technology can integrate the resources scattered in different places and work like a cloud server.