# Hash-Chain-Based Cross-Regional Safety Authentication for Space-Air-Ground Integrated VANETs +
###### Abstract  
With the increasing demand for intelligent traffic management and road network intelligent information services, the vehicular ad hoc networks (VANETs) combined with information of air, space and ground have outstanding advantages in coverage, reliable transmission, and resource richness. Due to the characteristics of heterogeneous, numerous nodes, and frequent cross-network flow, the space-air-ground integrated network (SAGIN) puts forward higher requirements for security. This paper proposes a cross-regional node identity management architecture based on the hash chain, combined with radio frequency (RF) fingerprint theory, to guarantee node identity security with a non-duplicated physical information identity authentication mechanism. At the same time, the blockchain consensus mechanism is simplified to achieve block recording and verification. OMNet ++, SUMO, and Veins co-simulation platforms are used to generate transactions for cross-regional traffic flow. Based on the Hyperledger-Fabric architecture, Kafka and PBFT consensus algorithms are simulated. The simulation results show that the average delay of a single transaction generated block is about 0.9 ms, which achieves efficient and low-latency authentication. hash chain; radio frequency fingerprint; space-air-ground integrated network; vehicular ad hoc networks; identity authentication +
Footnote †: journal: Applied Sciences  
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line-of-sight transmission for the ground information platform composed of vehicle nodes. The SAGIN structural system is complex and exists in an open communication environment, which is extremely vulnerable to eavesdropping and interception from malicious users [4]. Moreover, the large-scale cross-regional transmission in SAGIN makes the network more susceptible to threats such as data tampering at the forwarding nodes, longer transmission delays, and exhausted communication resources [5]. Given the above characteristics, in the process of aided driving through space-air nodes, the safety requirements of VANETs in an integrated environment of space-air-ground need to be considered more. Based on the basic idea of using digital pseudonyms as unique identifiers for identity verification without using any personally identifiable information [6], most of the current key management schemes of VANETs are designed based on the public key infrastructure (PKI) [7] It requires a long authentication time, massive certificate storage, and management overhead. In [8], a dynamic key distribution scheme for VANTEs is proposed. By sending revocation messages only to vehicles with the probability of communication with the revoked vehicle, the overhead cost is reduced, and the network use rate is improved. A secure and reliable key management method protocol (SA-KMP) is proposed in [9], which distributes the repository to each vehicle and RSUs. By incorporating the authentication mechanism into the key distribution scheme, the risk of denial of service (DoS) attacks, and the complexity caused by the PKI scheme are reduced. The high-level encryption technology also has the phenomenon of being compromised [10]. Once the above-centralized management system based on trusted third parties is attacked in the scenario of a node moving across regions, it is easy to cause communication blockage or even paralysis. Furthermore, the current PKI technologies for managing vehicle keys by different organizations in the VANETs are different and incompatible. It will be challenging for vehicles to interoperate when performing cross-regional authentication. Therefore, this paper proposes a cross-regional node identity management architecture based on the hash chain, combined with the physical identity information authentication mechanism to ensure the security of node identity.