# Practical V2I Secure Communication Schemes for Heterogeneous VANETs
## 2 Related Work  
Considering the security requirements of V2I secure communication in VANETs, it is natural to utilize encryption to realize confidentiality and digital signature to realize authentication, integrity,and non-repudiation. The traditional approach, named the signature-then-encryption method, is first to sign a message and then to encrypt it, or first to encrypt a message and then to sign it, named the encryption-then-signature method. [PERSON] first presented a new cryptographic primitive termed as signcryption [3], which simultaneously realizes the functions of encryption and digital signature. In addition, its cost is much smaller than the encryption-then-signature or signature-then-encryption techniques. [PERSON] et al. proposed the general constructions of signcryption [4] and [PERSON] et al. studied the formal proofs for the security of signcryption [5]. In addition, [PERSON] et al. proved the security of the scheme in [3]. The performance advantage of signcryption makes it widely studied and used. Up to now, signcryption and its extension schemes have been put forward in several cryptosystem, such as the PKI-based cryptosystem [6,7], identity-based cryptosystem (IBC) [8, 9, 10, 11, 12], and certifiateless cryptosystem [13, 14, 15]. Aggregate signcryption is one of the latest extensions of signcryption, which can combine multiple signcryption ciphertexts and verify them in batch. Compared with the traditional sequential verifications, it not only can save a lot of time, but also can save the computational, communicational, and storage cost. Hence, aggregate signcryption is very suitable for many-to-one mode of distributed communication, such as VANETs and routing protocol. Today, vehicles and RSUs are extremely heterogeneous and may be registered with different public key cryptosystems. To ensure the secure V2I communication between these extreme heterogeneous devices, cryptographic schemes should be constructed to provide authentication, confidentiality, integrity, and non-repudiation, so signcryption naturally becomes the first choice. So far, a few signcryption schemes for heterogeneous environments have been proposed [16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26]. Many of these schemes consider two mainstream public key cryptosystems PKI and IBC. In the PKI system, a certificate authority (CA) issues the digital certificates for users, which bundle the public keys and users' real identities. However, certificates management has become a burden due to the storage, revocation, and distribution of certificates. However, in IBC, the email addresses, telephone numbers, or social security numbers of users are used to produce the public keys. The users' private keys are provided by a trusted third party named private key generator (PKG). IBC solves the problem of certificates management and becomes a more promising public key cryptosystem. [PERSON] and [PERSON] put forward two heterogeneous signcryption schemes. The first one supports a sender in a PKI system to transmit one message to a receiver in an IBC and the second is opposite (i.e., from IBC to PKI) [21]. In addition, the paper gives a discussion on the multi-receiver constructions from PKI to IBC. Unfortunately, their schemes do not support non-repudiation and cannot resist insider attacks. Later, a heterogeneous signcryption scheme against insider attacks is proposed in [22]. However, it simply permits a user in an IBC to transmit one message to the recipient in a PKI system. Schemes presented in [23, 24] also do not allow users in a PKI system to send messages to recipient in an IBC. Recently, two new signcryption schemes are presented to support V2I mutual communication for heterogeneous PKI and IBC cryptosystem [25]. However, both schemes cannot protect the privacy of the senders. The scheme put forward in [26] gives a provable aggregate signcryption for heterogeneous PKI and IBC systems to improve the efficiency of computation and transmission.