# Negotiation-Free Encryption for Securing Vehicular Unicasting Communication
## 2 Related Work  
VANET plays an important role in future Intelligent Transport System ITS, secure trade-off between vehicles is very important as VANET supports safety-related applications. Because topology of the VANET changes rapidly, it is challenging to ensure real-time and security data transmission. A lot of techniques have been proposed to ensure secure privacy-preserving vehicular communications. [PERSON] et al. [13] proposed an efficient pseudonymous authentication scheme with strong privacy preservation (PASS) for VANETs. A novel scheme based on one-way hash chain is designed to generate the pseudoidentities of the pseudonymous certificates belonging to the same owner, and an efficient certificate-updating scheme is also proposed. [PERSON] et al. [14] proposed a distributed key management framework based on group signature to provision privacy in vehicular ad hoc networks (VANETs). An efficient cooperative message authentication protocol is developed to reduce the computation and communication overhead. [PERSON] et al. [15] proposed a decentralized authentication protocol which use the RSUs to establish a communication group and nodes belong to the group request secret member keys from the RSUs. [PERSON] et al. [16] proposed pseudonymous authentication-based conditional privacy (PACP) scheme, RSUs are also used to generate pseudonyms for anonymous communication. PACP allows vehicles to generate provably anonymous and computationally efficient pseudonyms to ensure conditional privacy. [PERSON] et al. [17] proposed a secure dual authentication technique with the capability of preventing malicious vehicles entering into the VANET system. A dual group key management scheme is also proposed to efficiently distribute a group key to a group of users and to update such group keys during the users' join and leave operations. [PERSON] et al. [18] proposed an Expedite Message Authentication Protocol (EMAP), which replaces the time consuming CRL checking process by an efficient revocation checking process. EMAP also uses a novel probabilistic key distribution, which enables non-revoked OBUs to securely share and update a secret key. [PERSON] et al. [19] proposed a cooperative authentication scheme that does not involve inter-vehicle interaction, an evidence-token mechanism is added to resist the free-riding attacks that do not use fake authentication efforts. [PERSON] et al. [20] proposed a lightweight and efficient strong privacy preserving (LESPP) authentication scheme by mainly using message authentication code (MAC) and symmetric encryption. The proposed scheme can reduce both computation and communication overhead. Sign messages which were used to sign in identity-based signatures can be omitted, this can further reduces communication overhead and avoids certificate management. [PERSON] et al. [21] proposed a new ID-based CPPA scheme for VANETs without using bilinear pairing, which provides the function of batch verification of multiple messages. The proposed scheme does not use bilinear paring but still supports both the mutual authentication and the privacy protection simultaneously. [PERSON] et al. [22] proposed a novel framework with preservation and repudiation (ACPN) for VANETs, in which a public-key cryptography (PKC) to the pseudonym generation is introduced, which ensures legitimate third parties to achieve the non-repudiation of vehicles by obtaining vehicles' real IDs. The existing ID-based signature (IBS) scheme and the ID-based online/offline signature (IBOOS) scheme are used, for the authentication between the road side units (RSUs) and vehicles, and the authentication among vehicles. These schemes lowered time costs in computational delay of the V2X authentication, and higher efficiency can be achieved. However, there are still many drawbacks to be improved (the complexity of the key negotiation, the costs of security certificate management, the long delays in negotiations, etc. ), and the unique features of Vehicle Networking have not been effectively used.