# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 4 Blockchain-Based Authentication Schemes in Vehicular Networks
### Consortium Blockchain-Based Authentication Protocols  
A consortium blockchain, also known as hybrid blockchain, is a combination of both private and public blockchain in which the read access can be open or restricted, and only a small group of nodes belonging to different organizations is responsible for making the consensus. Since consortium blockchains incorporate the best of public and private blockchains, that is, a mixture of decentralization with good level of trust at the same time, it has been the most popular blockchain type being implemented by researchers for IoV authentication. In such way, the authentication can be performed with a high degree of trust since only a group of trusted entities perform the consensus of the authentication data blocks, while guaranteeing an efficient performance in terms of resource utilization and authentication time delay due to the semi-decentralized nature of consortium blockchains. The authors in [128] optimized the Byzantine consensus algorithm by adopting time sequence and gossip protocol [129] to validate IoV information for correctness before adding them to the consortium blockchain. The use of gossip protocol, specifically the push-pull mode, enables faster data exchange among IoV nodes, as each two neighboring nodes can have the same information in one cycle. Two types of nodes are defined in the proposed scheme, i.e., Vehicle Communication Nodes (VCNs) and Roadside Communication Nodes (RCNs) in addition to the blockchain cloud platform used as storage for all IoV data. Due to their high computing and storage capabilities, RCNs are used as consensus-makers in the proposed Byzantine Consensus Algorithm with Time-sequence and Gossip protocol  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref. **} & \multirow{2}{*}{**Technique**} & \multicolumn{3}{c}{**Network Model and**} & \multirow{2}{*}{**Evaluation**} & \multirow{2}{*}{**Metrics**} & \multirow{2}{*}{**Features and Limitations**} & \multicolumn{1}{c}{**Privacy Preservation of Vehicle’s**} \\  & & & **Conterated** & & & & & & \\  & & & **(Other than Blockchain)** & & & & & & \\ \hline \multirow{8}{*}{
\begin{tabular}{c} [125] \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ - \\ \end{tab  
(BCA-TG). To ensure data integrity and authenticate the data sources, any data generated by a VCN or RCN must be agreed upon by more than half of the RCNs for the new block to be granted and linked to the blockchain. In the BCA-TG protocol, each RCN has an Update Information (UI) vector containing the Local Information (LI) of all RCNs in the consensus network as elements. Initially, the UI of each RCN will have only its own LI while all the other LI elements corresponding to the other RCNs are set to null. For example, if 5 RCNs are used for consensus making, the UI of \(RCN^{1}\) is initially: UI\({}^{1}\) = {\(L\)\(I\)\(I\)\(I\),0,0,0,0}. After which each RCN starts to communicate its UI vector with the neighbors in its view through the push-pull mode of gossip protocol until all RCNs have UIs with no null values. At this point, the element which forms more than half of the elements in the updated UI vector is considered the true information or the Consensus Information (CI) that will then be added to a new block and linked to the blockchain. The proposed scheme proves to have high fault tolerance since it can determine the CI even if the faulty or Byzantine nodes form 49% of the network. Moreover, their use of time sequence provides high scalability through its control over the entry and exit of nodes to/from the network and better convergence speed is achieved compared to the ordinary Byzantine consensus algorithm. The authors in [130] handled the cross-datacenter authentication issue in Vehicular Fog Computing (VFC) environment by proposing BLA--a Blockchain-based Lightweight Anonymous authentication scheme.