# Blockchain-Based Authentication in Internet of Vehicles: A Survey
## 4 Blockchain-Based Authentication Schemes in Vehicular Networks
### Public Blockchain-Based Authentication Protocols  
A public blockchain is an open access blockchain in which everyone can access, send, receive, and verify the different transactions of the blocks. Since it is a fully opened blockchain, even the vehicles can participate in the authentication process by looking up the ledger for the targeted authentication parameters. This provides a better utilization of the available computing resources in the IoV environment compared to restricting the authentication process to a few trusted nodes, thus a more decentralized, time efficient authentication process is achieved. These characteristics of a public blockchain have attracted many researchers to adopt it for IoV authentication. The authors in [120] contributed to address the authentication delay issues and time complexity in IoV network. The proposed work provides real-time authentication and adversary detection through the adoption of a public blockchain. The authors used the wireless channel characteristics, such as the received power and the Link Fingerprint (LF) along with the hash technology of blockchain to detect any intrusion in V2V communication in real-time. The main concept is that the wireless link between any two communicating vehicles has a unique fingerprint which is generated from the channel's power characteristics. As a result, the variation in the received power of the communicating vehicles must highly correlate, otherwise the communication path is intercepted, and an adversary is detected. Each vehicle uses the LF, a pseudo-random freshness parameter N, (that changes every time to prevent the system from replay attacks), and the hash of the previous block used to generate the hash value. The hash is then stored in its local memory and sent to the cloud to be stored in the publicly accessible ledger. A sending vehicle encapsulates the  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref. **} & \multirow{2}{*}{**Technique**} & \multirow{2}{*}{**Attack**} & \multirow{2}{*}{**Network**} & \multirow{2}{*}{**Evaluation**} & & \multirow{2}{*}{**Metrics**} & \multirow{2}{*}{**Features and Limitations**} & \multicolumn{1}{c}{**Privacy**} \\  & & & & **(Other than** & & & & **Limitations** & **of Vehicle’s** \\  & & & **Blockchain)** & & & & & **Identity? ** \\ \hline \hline \multirow{8}{*}{ \begin{tabular}{c} - Proof-of-Authory \\ consensus \\ - Elliptic curve \\ logarithmic problem \\ - - Elliptic \\ Curve Digital \\ - Signature \\ Algorithm \\ \end{tabular}  } & \multirow{8}{*}{**-**} & \multirow{8}{*}{**Impersonation**} & \multirow{8}{*}{**-**} & \multirow{8}{*}{**Critical**} & \multirow{8}{*}{**-**} & \multirow{8}{*}{**Provides mutual**} \\  & & & & & & & **with reduced** \\  & & & & & & & **the CA thus** \\  & & & & & & & reducing the overall \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & &  
packet with a header containing its hash value before being sent to the receiving vehicle. When the receiving vehicle gets the packet, it removes the packet header and looks up the hash value in the ledger to check the authenticity of the sender vehicle, if it exists, it accepts the package data; otherwise, an adversary is detected, and the packet is discarded. MICAz note--a hardware wireless sensor module--is installed on two vehicles to serve as a wireless communication interface in the V2V arrangement. Measurements are recorded indoor and outdoor in real-time and reported with the aid of MATLAB R2020a. The Pearson Correlation Coefficient [121] is computed to detect an adversary in the network when its value is less than or equal to 0.9. The scheme is also evaluated in terms of time complexity which is found to be as low as O(1) due to the simple and lightweight hash function used in their blockchain. The authors in [122] proposed a scalable blockchain-based protocol that deploys a dynamic proof-of-work consensus mechanism and Physical Unclonable Functions (PUFs) for authentication and trust establishment.