  With the development of artificial intelligence and self-driving, vehicular
ad-hoc network (VANET) has become an irreplaceable part of the Intelligent
Transportation Systems (ITSs). However, the traditional network of the ground
cannot meet the requirements of transmission, processing, and storage among
vehicles. Under this circumstance, integrating space and air nodes into the
whole network can provide comprehensive traffic information and reduce the
transmission delay. The high mobility and low latency in the Space-Air-Ground
Integrated Network (SAGIN) put forward higher requirements for security issues
such as identity authentication, privacy protection, and data security. This
paper simplifies the Blockchain and proposes an identity authentication and
privacy protection scheme based on the Hashchain in the SAGIN. The scheme
focuses on the characteristics of the wireless signal to identify and
authenticate the nodes. The verification and backup of the records on the block
are implemented with the distributed streaming platform, Kafka algorithm,
instead of the consensus. Furthermore, this paper analyzes the security of this
scheme. Afterward, the experimental results reveal the delay brought by the
scheme using the simulation of SUMO, OMNeT++, and Veins.
