# Hash-Chain-Based Cross-Regional Safety Authentication for Space-Air-Ground Integrated VANETs +
## 4 Cross-Regional Identity Authentication Model Based on the Hash Chain
### Authentication Process
(3) The SM-this determines the vehicle's cross-regional movement by collecting beacons messages sent by legal vehicles, which contain information such as speed, direction, and position. Collect \(n\) vehicles cross-regional movement per unit time to form \(n\) transactions. The transaction content includes the identity information of the SM-this, the transaction number, the identity of the SM-dest, the encrypted vehicle materials and the timestamp. (4) The SM-dest extracts the real-time RF fingerprint of SM-this, and compares it with the RF fingerprint features during registration, so as to judge the legitimacy of the identity of SM-this. (5) If it is legal, the SM node packages \(n\) transactions to create a block, and uses the Kafka consensus algorithm to add it to the hash chain and feedback the block result to the SM-this. At the same time, other SM nodes synchronize the contents of account books to obtain relevant information of cross-regional vehicles. (6) The SM-dest in the destination area obtains the identity of the vehicle nodes that will enter the new area according to the content of the transaction information on the block. If the information exists in the local ledger, it is legal, otherwise it is determined to be illegal and SM-dest refuses to provide services for it. In the study of individual identification using RF fingerprints, many scholars have conducted a lot of experiments on feature extraction. In this paper, the auxiliary classifier Wasserstein generative adversarial networks proposed in [33] is used to extract the RF fingerprint features of the wireless signal transmitted by the node and identify it. The deep learning-based method avoids the tedious manual design feature process. After the model is trained, the node identity can be quickly identified, and the accuracy rate can reach more than 95%. Compared with the traditional public-private key scheme, the RF fingerprint features of wireless signals is unique and inoperable. For the hash-chain-based authentication process mentioned above, the time delay includes: first, the time delay of the cross-regional transaction formed by verifying the identity of the vehicle nodes that need to cross the region per unit time. The second is the delay of packaging transactions into blocks and joining the hash chain. The third is the delay of multiple transmission processes. The specific delay formula is as follows:  
\[T_{hash-chain}=n*t_{identity}+(t_{prep}+t_{cons})+t_{transmission}*2 \tag{2}\]  
\(n\) represents the number of vehicle nodes cross-regional transactions collected in a unit time, \(t_{identity}\) represents the time delay for the SM node to verify the vehicle's identity, i.e., the RF fingerprint authentication time delay. \(t_{prep}\) and \(t_{cons}\) respectively represents the preparation delay of block generation and the delay required to reach consensus. \(t_{transmission}\) means waiting and propagation delay. According to the hash-chain-based authentication process, we conducted a security analysis for the space-air-ground integrated VANETs. Table 1 lists some of the security requirements and corresponding solutions. \begin{table}
\begin{tabular}{c c} \hline
**Requirements** & **Solutions** \\ \hline Authenticity & The RF fingerprint of the wireless signal is unique and non-cloneable, ensuring a reliable node identity. \\ \hline Data security & The data recorded on the hash chain have the characteristics of traceability, non-tampering, and non-repudiation. \\ \hline High efficiency & Improve network throughput and reduce block generation delay through Kafka distributed \\  & message queues. \\ \hline Against attacks & In the hash-chain system, because the hash value of the block is different from other nodes, it can be discovered in time when the node is attacked; even if the node is broken, there is a backup of the data about the node. \\ \hline Privacy protection & Use asymmetric encryption technology to protect the critical information of the block \\ \hline \end{tabular}
\end{table}