# Blockchain-Enabled Edge Intelligence for IoT: Background, Emerging Trends and Open Issues
## 3 Emerging Trends and Visions
### Blockchain-Based IoT Security  
No technology is perfect, neither is blockchain. The vulnerabilities of blockchain technology have drawn the attention of both industries and academics [75]. For example, a smart contract developer may make errors, and the related vulnerability could cause a \begin{table}
\begin{tabular}{c c c} \hline \hline
**Directions** & **Ref.** & **Contributions** \\ \hline \multirow{8}{*}{5G and Beyond} & [12] & Provide proof-of-concept for blockchain applications in 5G and beyond networks. \\ \cline{2-4}  & [13] & Investigate the potential of blockchain in 5G and beyond network for IoT. \\ \cline{2-4}  & [16] & Suggest guidelines toward blockchain enabled IoT with 6 Gcommunication. \\ \cline{2-4}  & [59] & Propose blockchain-enabled learning framework for 5G beyondscenarios. \\ \hline \multirow{3}{*}{Decentralized D2D} & [60] & Propose decentralized platform design for D2D computationcoordination in UDNs. \\ \cline{2-4}  & [47] & Optimize the decentralized D2D sharing and design the consensus for transactions execution. \\ \hline \multirow{8}{*}{Edge Computing} & [61] & Propose an energy-efficient IoT task offloading algorithm for blockchain-enabled edge computing. \\ \cline{2-4}  & [62] & Design a trustless hybrid human-machine ecosystem for industrial IoT based on crowd-intelligence. \\ \cline{2-4}  & [63] & Propose a novel service migration framework for flexible edge service. \\ \cline{2-4}  & [64] & Propose a trust-aware data trading system for MEC. \\ \cline{2-4}  & [65] & Design the joint resources allocation for blockchain-enabled MEC systems. \\ \cline{2-4}  & [66] & Propose a blockchain-based offloading strategy in MEC scenarios \\ \hline \multirow{3}{*}{Edge Caching} & [67] & Propose caching strategy for wireless blockchain networks. \\ \cline{2-4}  & [68] & Design an MEC-enabled wireless blockchain framework. \\ \cline{2-4}  & [69] & Propose an ultra-reliable drone-caching approach enabled by neural-blockchain. \\ \cline{2-4}  & [70] & Propose edge caching solutions based on FL. \\ \hline \multirow{3}{*}{Distributed NFV} & [73] & Propose a distributed NFV framework for management and orchestration based on the MEC-enabled blockchain. \\ \cline{2-4}  & [74] & Propose a novel distributed network architecture for fog nodes based on SDN. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Research directions and related literature on IoT communications. hard fork in the blockchain system. Moreover, consensus mechanisms have the risk of 51% vulnerability, which may cause malicious manipulations of transaction records. Therefore, researchers and system designers should consider security issues while investigating blockchain-based IoT systems. * _Authentication_: Authentication based on public-key cryptography is an effective solution to the security issue in IoT systems. A group signature scheme was proposed for block validation in MEC [76]. Moreover, the authentication of FL nodes was given in the Internet of health things [77]. The participating nodes were authenticated by the smart contract in the proposed FL framework. Furthermore, [PERSON] et al. [78] investigated the authenticity of emergency levels in healthcare cases. The delay of the MEC network was also optimized by them. * _Data Security:_ With the immutability of data records, blockchain has a nature of data security. Therefore, this topic was considered in most literature in this research area. For example, [PERSON] et al. [79] gave a secure data sharing scheme based on the consortium blockchain and smart contracts for vehicular networks. * _Data Privacy:_ In public blockchain systems, participants are anonymous because they are just hashes of public keys. Different from a public blockchain in which all records are visible to everyone, a permissioned or private blockchain, such as the Hyperledger Fabric, only allows authenticated entities to access the data on the blockchain. Furthermore, the zero-knowledge proof is another technique to make a transaction without revealing participants' information.