# Practical V2I Secure Communication Schemes for Heterogeneous VANETs
## 1 Introduction  
Smart transportation is one of the most important aspects of smart city, and vehicular ad hoc networks (VANETs) have recently been regarded as a promising smart transportation technique that can provide road safety, traffic management, and so on. VANETs consist of smart vehicles with on-board units (OBUs) and roadside units (RSUs). In VANETs, the vehicles can be regarded as mobile nodes and the communication between these nodes can be conducted by dedicated short-range communications (DSRC) technology [1]. There are two main communication ways: Vehicle to infrastructure (V2I) and vehicle to vehicle (V2V) [2]. V2V communication can exchange information among neighboring vehicles. V2I communication allows vehicles send messages to RSUs in driving. Vehicles or drivers can obtain the traffic information of a region or even a wider scope. After information integration, V2I provides comprehensive driving guidance and early warning services for each driver, which is more advantageous than V2V communication from this point of view. For example, if a traffic accident happened, the accident vehicles will firstly transmit the accident information to a nearby RSU; next, the RSU broadcasts the information to other RSUs and more vehicles in its management region. All kinds of messages can spread faster to prevent traffic jams because RSUs have higher power and strongerinformation broadcasting ability. Hence, V2I secure communication is a promising technology and attracts more and more attention. However, a critical problem is the security of V2I communication. Generally speaking, confidentiality, authentication, integrity, and non-repudiation are the key security requirements for secure V2I communication. Confidentiality can keep messages secret except for those who are authorized. Authentication and integrity can ensure the messages are not tampered by any unauthorized user. Non-repudiation can prevent the denial of prior behaviors. Generally, encryption can be used to realize confidentiality and digital signature can be used to realize authentication, integrity, and non-repudiation. Due to the openness of wireless communication in V2I, an adversary can easily control the communication links and modify session messages, which may lead to serious consequences. Hence, the above security requirements are the main concerns for V2I secure communication and are worth studying urgently. In the paper, considering the aforementioned security attributes of V2I communication, we construct four practical bi-directional signcryption schemes, which offer heterogeneous V2I secure and efficient communication, in which the vehicles and the RSUs are registered in public key infrastructure (PKI) or identity-based cryptosystem (IBC), respectively. For this purpose, we mainly combine the signcryption and aggregation techniques to construct our schemes and permit the communicating parties sharing the same system parameters to achieve high efficiency according to current practices and traditions. To be specific, two many-to-one signcryption schemes can realize \(n\) vehicles in PKI/IBC system transmit messages to an RSU in the IBC/PKI system, which fit into the scenario where an RSU might receive multiple messages from different vehicles at almost the same time. In turn, two one-to-many signcryption schemes can support an RSU in PKI/IBC system transmitting one message \(m\) to \(n\) vehicles in IBC/PKI system, which applies to the scenario where an RSU broadcasts one message to multiple vehicles. All schemes have been proved to be indistinguishable against adaptive chosen ciphertext attacks (IND-CCA2) and existential unforgeability against adaptive chosen messages attacks (EUF-CMA) based on two difficulty assumptions of decisional Diffie-Hellman problem (DDHP) and computational Diffie-Hellman problem (CDHP), respectively. The main contributions of this work are summarized as follows:  
1.