# Blockchain-Based Distributed Computing Consistency Verification for IoT Mobile Applications
## 5 The Proposed BDCA  
### System Model  
The architectural diagram depicted in Figure 1 illustrates the configuration of BDCA, comprising three distinct consortium blockchains based on Hyperledger Fabric technology: the source chain (\(SC\)), the target chain (\(TC\)), and the audit chain (\(AC\)). The innovative model BDCA enables the secure and seamless exchange of data between the two different chains while ensuring data integrity through the implementation of an audit chain (\(AC\)) for data consistency verification as well as maintaining the decentralized feature of BDCA [36]. To further enhance the reliability and functionality of BDCA, three smart contracts are deployed within the system, each specifically allocated to \(SC\), \(TC\), and \(AC\), respectively. The four principal entities comprising BDCA are IoT devices (\(DO\)), source chain (\(SC\)), target chain (\(TC\)), and audit chain (\(AC\)) with each entity bearing unique responsibilities and obligations as follows:  
* _IoT device (\(DO\)):_\(DO\) is an entity that is responsible for processing and storing the original data \(M\), and initiating data update requests to the source chain (\(SC\)). To ensure the security and privacy of the data, \(DO\) preprocesses \(M\) into blinded data \(M^{*}\) before generating authentication tags for \(M^{*}\). Once \(DO\) has generated the authentication tags for \(M^{*}\), it transfers the blinded data and corresponding tags to the audit chain (\(AC\)) for secure storage. Within the BDCA model, there are two distinct \(DO\) entities, namely \(DO_{S}\) and \(DO_{T}\), which are deployed within the source chain (\(SC\)) and target chain (\(TC\)), respectively. * _Source chain (\(SC\)):_\(SC\) is an entity that serves as the primary repository for data received from \(DO\) and facilitates the exchange of data with the target chain (\(TC\)). Upon receiving data update requests from \(DO_{S}\), \(SC\) is responsible for updating the data accordingly and synchronizing the data updates with \(TC\) to ensure consistency across the two chains. In addition, \(SC\) is programmed to respond to audit challenges issued by the audit chain (\(AC\)) by generating an audit proof that verifies the consistency and accuracy of the data stored within the system. Once the audit proof is generated, \(SC\) sends it to \(AC\) for data consistency verification, ensuring that the data remains secure and reliable. * _Target chain (\(TC\)):_\(TC\) is an entity that is responsible for receiving data from the source chain (\(SC\)) and facilitates data exchange between the two chains. Upon receiving data update requests from \(SC\), \(TC\) updates the data as required, ensuring that the data remains consistent across both chains. Like \(SC\), \(TC\) also responds to audit challenges from the audit chain (\(AC\)) by generating storage proofs that verify the integrity and accuracy of the data stored within the system. Once the storage proof is generated, \(TC\) sends it to \(AC\) for data consistency verification, ensuring that the data remains secure and reliable. * _Audit chain (\(AC\)):_\(AC\) is an entity that is established and overseen by national regulatory authorities. \(AC\) is responsible for conducting data consistency verification between the source chain (\(SC\)) and the target chain (\(TC\)) based on the audit proof and storage \begin{table}
\begin{tabular}{c c} \hline \hline
**Notations** & **Descriptions** \\ \hline \(M\) & The original data \\ \(M^{*}\) & The blinded data \\ \(M^{*^{\prime}}\) & The updated data \\ \(d\) & A public key of \(DO_{i}\) \\ \(\{e,u\}\) & A private key of \(DO_{i}\) \\ \(n\) & System security parameter \\ \(Tx_{1}\) & Data uploading transaction \\ \(Tx_{2}\) & Data updating request transaction \\ \(DO_{\delta_{0}}\) & The leader of all the signers in blockchain \\ \(DO_{S}\) & The IoT device of \(SC\) \\ \(DO_{T}\) & The IoT device of \(TC\) \\ \(\omega\) & The threshold number of signers \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Notations and descriptions.