## 2 Related Work  
Many security methods are proposed to support authentication for all exchanged periodic information in V2X. Public Key Infrastructure (PKI) authentication methods were proposed to support message authentication using digital signatures and identity authentication using a certificate [13]. The digital signatures in PKI provide authentication and integrity, using long size certificates incurs high communication and computation overhead. Due to the high-cost of PKI-based methods, some identity-based (ID-based) authentication methods are proposed in [14; 15; 16; 17]. In [14], [PERSON] et al. proposed an identity-based privacy-preserving authentication method for V2X. In [15], [PERSON] et al. designed a new ID-based authentication method using Elliptic Curve (ECC) for authentication and privacy-preserving. These ID-based methods require less communication overhead to support authentication and preserve privacy. In [16], [PERSON] et al. presented an efficient anonymous authentication method using message recovery and signatures to enhance system efficiency. In [17], [PERSON] et al. proposed the batch verification method based on identity authentication for V2X and defined different security risks. In [18], [PERSON] et al. improved the proposed [PERSON] et al. [17] methods, by proposing a secure batch verification method based on ID, without bilinear pairings. Though these ID-based solutions could eliminate the PKI problems, it suffers from a key escrow problem. To overcome the PKI overhead and the key escrow problems of ID-based solutions, many certificateless (CLS) signature methods were proposed [19; 20; 21; 22; 23; 24]. [PERSON] et al. [19] proposed a privacy-preserving aggregated signatures method for V2V communication. In this method, only the partial private key of the users was generated by a trusted Key Generator Center (KGC). A secret random value was picked by each user and combined with the partial private key to generate a new private key. Therefore, the user's private keys were not stored at the KGC. In certificateless CPPA methods, vehicles do not need to store certificates to guarantee the authenticity of the used public keys. [PERSON] et al. [20] proved that the proposed method in [19] was not secure against the passive malicious KGC, using the existing security model. [PERSON] et al. [21] proposed a new efficient certificateless aggregate signature protocol for V2X, and proved the security level using the random oracle model. Additionally, the proposed protocol was computationally more efficient due to its constant pairing operations. After discussing the vulnerabilities of malicious-but-passive KGC attacks, [PERSON] et al. [22] presented an improved protocol. They presented a new security method, based on authentication using group signatures for V2X. In this method, a single manager issues the secret keys for each vehicle. [PERSON] et al. [23] proposed a new Conditional Privacy-Preserving Authentication (CPPA) method, based on bilinear pairing cryptography, to improve identity-based authentication in V2X. However, this method could not prevent the message modification attacks in which an attacker could repeat the transmission of old messages after modifying its content. In [24], [PERSON] et al. proposed the first protocol for group signature, based on bilinear pairing. This group signature protocol suffers from high computation and communication cost. All mentioned methods in [19; 20; 21; 22; 23; 24], employ the bilinear pairing cryptography for a single cell or group authentication. It also limits the network scalability and availability, and suffers from high computation time and complexity. We summarize the advantages and disadvantages of the security protocols [19; 20; 21; 22; 23; 24] in Table 1.  
In this study, we proposed a Multi-Zone Authentication and Privacy-Preserving Protocol (MAPP), based on bilinear pairing cryptography. The proposed protocol supports privacy-preserving by generating pseudo-identities to hide the vehicle's real identities.