## 2 Related Works
### Literature Reviews
#### 2.1.1 Authentication Protocol for Vehicle Communication  
Authentication is considered a basic security service that allows subjects to mutually authenticate with other subjects [5; 6; 7; 8; 9]. In 2007, [PERSON] et al. [10] suggested an authentication protocol while using a group signature based on bilinear pairing. In their protocol, the verifier can verify multiple signatures simultaneously, which improves authentication efficiency. However, [PERSON] et al. [11] pointed out a significant flaw in [PERSON] et al.'s protocol, that validation required at least two pairing operations that could not be extended. In addition, their protocol uses many exponential operations that require complex computing. Therefore, they suggested an authentication protocol based on bilinear pairing and used addition operation, which is simpler than exponential operation. In 2013, [PERSON] and [PERSON] [12] found that [PERSON] et al.'s proposed scheme also has security weaknesses. They demonstrated that [PERSON] et al.'s protocol cannot achieve the signature non-repudiation and is insecure against replay attack. Moreover, [PERSON] et al.'s scheme cannot provide security to masquerade and tracking attacks. However, [PERSON] et al. [13] proved that [PERSON] and [PERSON]'s protocol is insecure to the impersonation and tracing attacks and violates the non-repudiation. Further, [PERSON] et al. [14] also found an impersonation attack in [PERSON] and [PERSON]'s protocol. After that, [PERSON] et al. [14] proposed a secure authentication scheme for VANETs with batch verification to overcome [12]'s security weaknesses. Unfortunately, [PERSON] et al. [15] pointed out that [14]'s protocol cannot defeat against modification, replay, and impersonation attacks. Then, [PERSON] et al. [15] designed a novel secure protocol using Elliptic Curve Cryptographic (ECC) for vehicle communication. [PERSON] et al. [16] analyzed the protocol in [15] and concluded that using complex cryptographic functions can result in enormous operational costs and, consequently, the system faces network disruption problems. Therefore, they proposed a system to distribute pseudonymized signatures to verify user identities. In 2014, [PERSON] et al. [17] proposed a trust-extended authentication scheme in VANETs. Under their protocol, vehicles are divided into three types and they only used hash and exclusive-or functions to create lightweight communication. However, [PERSON] et al. [18] found out that [PERSON] et al.'s protocol cannot guarantee privacy-preserving and is vulnerable to impersonation and insider attacks. They also argued that the assumption of TPD is strong. Therefore, [PERSON] et al. proposed a more secure authentication protocol to improve [PERSON] et al.'s protocol. They use an ECC to protect entities' real identities and protect against internal attacks. In 2019, [PERSON] et al. [19] pointed out that [PERSON] et al.'s proposed protocol cannot prevent identity guessing and impersonation attacks and also cannot guarantee user's anonymity. In 2017, [PERSON] et al. [1] proposed a personal information protection system based on distributed aggregation to conditionally block user's anonymity. However, this method takes more time to verify the signature, so the recipient must spend more time immediately verifying the correctness of the message. In 2019, [PERSON] et al. [4] proposed a secure message confirmation in vehicular cloud environment. They are pointed out that [PERSON] et al's protocol [16] has a security flaws using side channel attack over the OBU and TPD. Therefore, they suggested a more secure protocol for overcoming computational limitations of OBU and TPD through cloud computing. However, we revealed that their proposed protocol does not defeat several malicious attacks, such as session key disclosure attack and masquerade attack and so on. Additionally, their protocol does not provide privacy preserving and mutual authentication and has a correctness problem.