Privacy Preserving Partially Homomorphic Encryption with Optimal Key Generation Technique for VANETs

In recent days, vehicular ad hoc networks (VANETs) has gained significant interest in the field of intelligent transportation system (ITS) owing to the safety and preventive measures to the drivers and passengers. Regardless of the merits provided by VANET, it faces several issues, particularly with respect to security and privacy of users/messages. Because of the decentralized structure and dynamic topologies of VANET, it is hard to detect malicious or faulty nodes or users. With this motivation, this paper designs new privacy preserving partially homomorphic encryption with optimal key generation using improved grasshopper optimization algorithm (IGOA-PHE) technique in VANETs. The goal of the proposed IGOA-PHE technique aims to achieve privacy and security in VANET. The proposed IGOA-PHE technique involves two stage processes namely ElGamal public key cryptosystem (EGPKC) for PHE and IGOA based optimal key generation process. In order to improve the security of the EGPKC technique, the keys are optimally chosen using the IGOA. Besides, the IGOA is derived by incorporating the concepts of Gaussian mutation (GM) and Levy flights. The experimental analysis of the proposed IGOA-PHE technique is examined in a wide range of experiments. The resultant outcomes exhibited the maximum performance of the presented IGOA-PHE technique over the recent state of art methods.


Introduction
Vehicle ad hoc networks (VANET) are developed as a part of Mobile Adhoc Network (MANET) [1,2] applications. VANET is deliberated as a significant method for intelligent transportation systems (ITS) [3]. Recently, VANET was an emphasis of many scientists in the field of wireless mobile transmission. The goal of VANET has to give an inter vehicle transmission and road side unit (RSU) to vehicle transmission for increasing safety of the road and enhance local traffic flow and the performance of road traffic via giving timely and accurate data to road clients [4]. In VANET, vehicle is utilized as network nodes, as shown in Fig. 1. The OBU & RSU in VANET develops a link between itself using dedicated short range communication (DSRC) from the single/multi hop transmission [5]. VANET offers many applications and services to the user, all of them are involved by infotainment, navigational aid, and security of the driver [6]. Though the interest around the significant advantages of VANET is developing, the dynamic nature of VANETs (vehicle could leave & join willingly) together a multitude of scheme and application interrelated requirement makes it highly difficult for designing an effective method to ensure vehicle privacy [7]. Privacy represents vehicle privacy (driver) and vehicle position.
If a vehicle sends a message, nobody (but appropriate authority) can define the position/identity of the vehicle from the message a vehicle transmits. Simultaneously, whole messages transmitted by the vehicle must be valid beforehand processed further. Till this problem is resolved to the optimal fulfillment of the user, extensive placement of VANET could not be performed. Verification should be attained at 2 levels, initially at node level, represents node verification, and next at message level represents message verification [8].
The fundamental standard of message authentication could be shortened by signing a message by the sender and later verify the integrity & authenticity of the message at the receiver end.
Particular verification needs like scalable and strong authentication, effective and scalable certificate revocation, lower computation overhead should be tackled and resolved for ensuring secure transmission in VANET. Guaranteeing privacy of vehicle (driver) is a major problem in which an effective solution should be made or else an adversary can track vehicles traveling route by analysing and capturing it message [9] and identify the vehicle (driver) might contain serious impact for the drivers.
To tackle this problem, several scientists have projected procedures where vehicles can utilize pseudonym rather than their real identity in transmission simultaneously allowing authorities for extracting the real identity from pseudonyms to punish and trace mischievous vehicles [10].
This protocol is known as conditional privacy-preserving protocol. Allocating pseudonyms to vehicles and modifying them regularly is another approach utilized for ensuring privacy of the vehicle. For maximizing privacy, vehicles should modify pseudonyms more often though the occurrence of these changes remains uncertain. Features like storage size and availability play a significant part in defining the rate whereat the pseudonym must be modified [11]. Most of the studies in the survey tackling privacy, security, and authentication utilize TA to obtain and load OBU & RSU by security variables like pseudonyms, keys, and certificates. Fig. 2 illustrates the secure data transmission in VANET.

Fig. 2. Secure data transmission in VANET
Conventional methods to authenticate and secure message dissemination, mainly depending upon key management and message encryption, could assure secure message interchange among destination pair and known sources. This method cannot directly be employed in terms of VANET because of the dynamics of VANET. Message dissemination in VANET could be susceptible to insider attacks (viz., attacks from valid VANET members), that might damage the content of disseminated message or transmit malicious message. Therefore, guaranteeing the authenticity & integrity of the transferred message in VANET is a significant problem. This paper designs new privacy preserving partially homomorphic encryption with optimal key generation using improved grasshopper optimization algorithm (IGOA-PHE) technique in VANETs. The goal of the proposed IGOA-PHE technique aims to achieve privacy and security in VANET. The proposed IGOA-PHE technique involves two stage processes namely ElGamal public key cryptosystem (EGPKC) for PHE and IGOA based optimal key generation process.
To improve the security of the EGPKC technique, the keys are optimally chosen using the IGOA. Above and beyond, the IGOA is derived by incorporating the concepts of Gaussian

Related works
Al-Shareeda et al. [12] presented a VANET based privacy preserving communication scheme (VPPCS) that meets the requirement for contextual & content privacy. It leverage the elliptic curve cryptography (ECC) as well as identity based encryption system. They have executed comprehensive security analyses (random oracle module, BAN logic, security attribute, and security of proof) to verify and validate the presented system. The analyses have displayed that this system is secure and also displayed to be efficient in a calculation. Cui et al. [13] proposed an effective and privacy preserving data downloading system for VANET, depending upon the edge computing model. In the projected system, an RSU could detect the common data by examining the encrypted request transmit from neighbouring vehicles with no need for sacrificing the privacy of their downloaded request. Additionally, the RSU stores the common data in near qualified vehicle named ECV. When a vehicle needs to upload the current data, it could upload it directly from the adjacent ECV. This technique raises the uploading performance of the scheme.
Alfadhli et al. [14] proposed a light weighted multi factor verification and privacy preserving security solution for VANET. Additionally, it removes the heavyweight dependency on the scheme key through decentralizing the broad area of CA to local areas and attains strong controller of the domain key. Ali and Li [15] proposed an effective ID-CPPA signature system depending upon bilinear map for V2I transmission. This raises the efficacy by signing and authentication of message at the RSU is executed. Moreover, this ID CPPA signature system supports the batch signature authentication technique, that decreases the computation overhead on RSU thus allows it for authenticating a huge amount of traffic interrelated messages in many vehicles in area with higher traffic density.
Wang et al. [16] proposed a novel identity based anonymous authentication system. In this system, the master key of the system won't be directly set up in TPD. For generating private key of the vehicle, further privacy is needed, and this privacy is given using RSU. Thus, revoking a malicious vehicle in VANET is effective, hence the RSU should end making the current privacy for the vehicle. Additionally, the signature authentication method includes no bilinear pairing operation, creating the authentication procedure highly effective. Wang et al. [17] proposed a hybrid CPPA protocol depending upon PKI certificate and identity based signature. In this system approach, the TA allocates the exclusive long term certificate for all the listed nodes. Vehicles with valid certificates could employ the anonymous short term identity in the present RSU for signing security relevant messages. The identity based signatures avoid CRL checking and the complicated bilinear paring operations.
Moni and Manivannan [18] proposed a privacy preserving authentication, scalable, distributed, low overhead system for VANET. This method utilizes MHT to authenticate RSU and MMPT for verifying the vehicles. In Benarous et al. [19], a novel privacy preserving solution for pseudonym on-road on-demand refilling is presented whereas the vehicle anonymously authenticates itself to the local authority subsidiaries of the central trusted authority for requesting a novel pseudonyms pool. This technique contains challenge based authentication and anonymous ticket. Al-shareeda et al. [20] presented an identity based CPPA system that supports the batch authentication procedure for the concurrent authentication of many messages with every node.

The Proposed IGOA-PHE Technique
The overall working principle involved in the proposed IGOA-PHE technique is here. It is stated that the IGOA-PHE technique follows a 2-stage process namely EGPKC for PHE and IGOA based optimal key generation process. These processes are neatly elaborated in the following subsections.

Design of EGPKC Technique
Generally, it is stated in 1985 using discrete method cause problems to constrained areas (partial HE technique). It has key decryption, generation, and encryption operations. Usually, this technique has private key (an arbitrary amount) ∈ qi ′ * by its corresponding public key ≡ (g ′ ) mod , whereas g ′ identify the generator to 1 using prime order ′ . Therefore, the novel involvement, to optimize the corresponding private key with the help of new hybrid method. An optimization handles creation of an optimum key this indeed enhances and states the security emergency. Moreover, an encryption message m ∈ 1 & public key is determined by 1 ≡ (g ′ ) n mod , 2 ≡ m mod , whereas denotes random amount.
Likewise, the decryption ciphertext Most of this technique takes an equivalent ciphertext by selecting a plaintexts attack for every probabilistic polynomial time adversaries . Also, the message encrypting arbitrarily in two different messages assured by , to identify the elected message is increased to random resolving. For considering, the ElGamal cryptosystem is determined by the game module with the challenger and opponent .
 Initially, elects two separate messages as m 0 , m 1 ∈ 1 and forward it to ′ .
 The calculated challenge ′ analyses on .
 For calculating a guess as provides ′ and forward it return to ′ . Now, becomes a success when ′ = otherwise fails.
In Above mentioned game, consider recognizes ′ , (g ′ ) i , (g ′ ) & (g ′ ) m but cannot get right access for and ri'. Now, the success possibility of probabilistic polynomial time challenger for achieving is high to random guessing as given in Eq. (1): In Eq. (2), denotes success possibility and represent trivial improvement. Eventually, the ciphertext along with an optimum private key is revealed in MAC.
Generally, the MAC frames are modelled to maintain minimal sophisticated form by a sufficient strength for declaring stable transmission on the noisy channel. Also, each successive protocol layer is added to the frame from layer specific footers & headers. The MAC structure has four frames.
 Initially, the beacon frame, employed with the coordinator to transfer beacons.
 In 2nd, the data frame, utilized to broadcast the whole data.
 In 3rd, the acknowledgment is used for assuring the efficient frame is delivered.
 Laslty, the MAC command frame is utilized for managing the whole MAC peer entity control transmissions. Now, the data frames transmit the MAC payload and aforementioned procedure is finished in the data frame. MAC payload executes the ciphertext with corresponding transmissions and private keys. On the recipient side, an equal decoder process takes place and eventually, attains the original data.

Design of IGOA for Optimal Key Generation
The private key in ElGamal cryptosystem is enhanced to accomplish the accurate ciphertext.
A novel technique is developed; where it is implemented to create the ciphertext using numerical values. In general, the proposed ciphertext has numbers (1, 2, 3. . .), alphabets (a, A, b, D, … ) and special characters(!, @, * , … ). Based on the penalty is set, (i) once the ciphertext using numeric values are attained, penalty = 0 (ii) after the ciphertext is attained with alphabetical and special characters, penalty could reduce in interval. The aim is to achieve a decreased penalty (given in Eq. (2), e.g., the ciphertext should be in numerical values.
Grasshopper is deliberated as pest depending upon the loss they impose on vegetation and crops. In place of performing separately, grasshopper creates few biggest swarms amongst all living beings. The impact of an individual in a wind, swarm, food source, and gravity affects swarm motion. The GOA is a new SI based metaheuristic method that is stimulated using longer range and sudden movement of adult grasshoppers in a group. Metaheuristic algorithm reasonably separates the search procedure as to exploitation & exploration phases. The longer range and sudden motions of the grasshopper denote exploration stage, and local motions for searching for an optimal food source represent exploitation stage. A numerical module for this behavior is given in Mirjalili [21] can be denoted as: Whereas denotes location of grasshopper, indicates social interaction in a group, represents force of gravity performing on grasshopper, and signifies wind direction. By extending , & in (1), the formula is given by: Whereas Since grasshoppers rapidly detect comfortable zone and show poor convergence, the impacts of wind and gravity are far weaker compared to the relationship among grasshoppers, means numerical module must be altered by: Whereas max denotes maximal value (equivalent to one), min represents minimal value  Whereas 2 denotes difference for every member of the population. This operation is additionally decreased for generating a single n-dimension arbitrary parameter by locating the mean value to 0 and SD to one. The arbitrary parameter created is employed for the common formula of metaheuristic method can be denoted by where ( ) denotes Gaussian step vector made by Gaussian density function using α as Gaussian arbitrary amount among zero and one.
For obtaining a tradeoff among the exploitation and exploration abilities of metaheuristic method, LF method is utilized for updating search agent location that can be given by: where v denotes novel location of th search agent afterward upgrading and denotes random vector in zero and one ⊕ indicates dot product (entry wise multiplication).
As mentioned, the range of search agents is critical for metaheuristic method, since diversity provides the population a robust search ability to global optimal. In IGOA, GM method has been applied for increasing the range of GOA population. The altered numerical module is introduced by: Afterward the location of th grasshopper i is upgraded, Levy flight method would be adapted for generating a novel candidate solution that can be given by: whereas X * denotes novel location of ith grasshopper afterward upgrading and ( ) denotes d-dimension arbitrary vector is zero and one. Since Levy flight is an arbitrary procedure where the jump size follows the Levy likelihood distribution functions, the novel candidate solution is made using Levy flight method is a higher likelihood of jumping beyond local optimal and attains optimum solutions. For ensuring the population quality, search agents using high fitness would be retained in the population.

Performance Validation
This section validates the performance of the proposed IGOA-PHE technique with other techniques interms of different measures.

Conclusion
This