Secure Communication in VANET BroadcastingMuhammad Jafer, M. Arif Khan, Sabih ur Rehman and Tanveer A. Zia

School of Computing and MathematicsCharles Sturt University, Australiamjafer@ieee.org,{mkhan, sarehman, tzia}@csu.edu.au,

Abstract

Broadcasting is a communication mechanism utilized in VANET architecture that facilitates in disseminatedof public information to help reduce traffic jams/congestions. The authentic and genuine nature of publicinformation is required to be maintained to avoid broadcasting of false information causing mass panic andhysteria. Therefore, it is of utmost importance to secure the broadcasting information so that an intruderis unable to alter any information without compromising public nature of the information. In this paper,we have proposed a secure broadcasting architecture consisting of different layers stacked together indifferent formation according to operating modes. A real-time simulation model is developed in Python, whilesimulations are run on a supercomputer for the purpose of gathering results for highway environments. Wecompare the results of the proposed secure highway architecture with unsecure architecture. Overall, theresults show delayed propagation time due to the availability of multiple information packets as well asprioritization of these information packets. However, there was no significant difference in retransmissionof different information packets when compared with either different broadcasting probability or unsecurehighway scenario, which indicates an effective as well as efficient, secure broadcasting architecture.

Received on 15 November 2018; accepted on 11 December 2018; published on 21 December 2018Keywords: VANETs, Secure Broadcasting, Network Coverage, Information Retransmission, Public Information

Copyright © 2018 Muhammad Jafer et al., licensed to EAI. This is an open access article distributed under the terms of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/), which permits unlimited use, distribution and reproduction in any medium so long as the original work is properly cited.

doi:10.4108/eai.10-1-2019.156243

1. IntroductionThe revolutionary concept of connecting physicaldevices to the internet is a step towards increasingbetter services and products for end-user satisfaction.Among these devices, such as refrigerators, televisions,smart washing machines and many more, vehicles areone of the most important devices for modern-daycommuters. Therefore, vehicles are at the forefront ofnew research capable of solving challenges related totraffic safety, congestion, accidents, and pollution [1–3].The most important concept introduced in recent timesis to establish a new type of mobile ad-hoc network forvehicles known as Vehicular Ad-hoc Network (VANET)[4]. In VANETs, the communication link between vehi-cles change frequently making the topology dynamic

∗Corresponding author. Email: mjafer@ieee.org

and vulnerable to security risks, which are the primaryfocus of our research.Moreover, there are two main types of communica-tion supported in VANETS namely: Vehicle-to-Vehicle(V2V) and Vehicle-to-Infrastructure (V2I) communi-cation. In general, V2V communication is establishedamong vehicles, whereas in the V2I scenario com-munication link is established between a vehicle andany roadside infrastructure, commonly known as RoadSide Units (RSUs). In addition to this, communicationscenarios in VANET can also be categorised as Point-to-Point (P2P) and broadcasting (BC) [5]. P2P com-munication can be defined as sharing the informationbetween two vehicles. In this scenario, one vehicle actsas a source and the second vehicle acts as a destination.In BC scenario, a vehicle transmits information to allvehicles within a certain geographical area. The BC sce-nario used in this paper is different than the commonlyused BC scenario in mobile wireless communicationwhere a transmitter broadcasts different informationfor different users. In this paper, we use BC as a source

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vehicle broadcasting the same information for multipleother vehicles.We also classify the information to be transmittedinto two categories private and public information asexplained below.Private Information :- We consider information as pri-vate, transmitted using P2P communication system, ifit is intended only for one single vehicle or it requirescertain decryption process to extract the informationfrom the transmitted signal. For the sake of simplicity,we assume that private information is intended onlybetween two vehicles that resemble the P2P communi-cation scenario defined above.Public Information :- On the other hand, public infor-mation is defined as the information available for anyvehicle within the network and it does not require anydecryption process to extract the information from thetransmitted signal. This scenario resembles BC commu-nication in VANETs as defined above.It is of great importance to transmitting authentic infor-mation whether public or private, therefore it is crucialto secure the information. Unsecured information espe-cially public information can be misused causing masshysteria and traffic jams. Whereas, when information issecured, it is difficult for intruders to alter the originalmessage and hence lowering the risk of creating publicpanic(s).The focus of this paper is to investigate and proposea secure broadcasting architecture for VANETs. Theproposed secure broadcasting architecture facilitates inthe implementation of strategies that avoid temperingof information during transmission. To the best ofour knowledge, there currently exists no publicationsrelated to research studies proposing secure broadcast-ing systems or architectures. However, there is sig-nification research studies as well as publications insecure P2P communication. This paper builds on thelessons learned from secure P2P communication archi-tectures by applying them to secure public informationin VANET broadcasting.Following list consists of three main contributions putforward in this paper:

• Identification and categorization of securitychallenges related to broadcasting in VANETs.

• Proposing of a layer based secure broadcastingarchitecture to counter alteration in informationduring broadcasting.

• Implementation of the proposed secure broad-casting architecture and collecting results relatedto credibility index with respect to propagationtime required by an information packet, Pinf o toachieve network coverage.

The rest of the paper is organized as follows. Section 2contains literature review of previous research, whereas

Section 3 describes the system model that is used inthis study. A discussion regarding proposed securebroadcasting architecture is contained in Section 4,while operational flow of the architecture is presentedin Section 5. In section 6, the numerical results arepresented in detail. Finally, Section 7 concludes thepaper.

2. Related WorkThe main focus of this paper is to extend thesecurity principles and techniques available in P2Pcommunication to VANETs BC. Some of the majorsecurity challenges in VANET are bogus information,ID disclosure, and Sybil attacks. There are a numberof solutions available for these security threats inthe literature such as [6–13]. However, one commonchallenge in the literature is that it is mainly focused onP2P mobile ad-hoc networks. In order to integrate thesesecurity features in VANET BC, we have classify thesefeature into three groups: Authentication, Anonymityand Availability of resources, which is inspired by workput forward in [4, 14–16].Authentication is a process of validating both senderand associated message by receiving vehicle [14].The validation process requires sender identification,which is defined by different properties such aslocation, direction, speed, and owner of the vehicle.The authentication mechanism helps to establish thereliability of the sender’s information, which ultimatelyprovides the mechanism facilitating prevention of Sybilattacks in VANETs. In addition to this, the process ofanonymity dictates hiding sender information as well asencrypting this information to make it unreadable forunintended users. Sender vehicles that are either sourceor relay vehicles may be willing to share informationprovided a mechanism to avoid tracking of vehicles orsharing actual vehicle information. On the other hand,a secure system is also required to incorporate fault-tolerant design, resilient to attacks as well as survivalprotocols so for the purpose of remaining availableand operational in the presence of faults or maliciousattacks [14, 17]. These three distinct groups of securitythreats are further explored with respect to P2P and BCsystems in the following sections:

2.1. Security in Point-to-Point (P2P) CommunicationA Point-to-Point (P2P) communication involves atminimum two vehicles, namely source and destination.Source vehicle transmits information intended for adestination vehicle, which employs a trust mechanismto establish the legitimacy of the received information.In [18], trust is based on a process called authenticationthat helps in correctly identifying source vehicle. Thisauthentication process consists of three different types,namely ID authentication, property authentication, and

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location authentication. ID authentication uses uniqueIDs, which are either license number or chaises numberof a vehicle, for identification of a vehicle. The propertyauthentication facilitates in identifying the type ofsources, such as a vehicle or a traffic signal, on the otherhand, location authentication identifies the location of asource allowing receiving vehicles to validate receivedinformation. Authentication is an effective process ofidentifying the source as well as validating transmittedinformation. However, this would compromise theanonymity of a source vehicle providing a convenientway of tracking as well as identifying the vehicle andits passengers.In [19], a centralized system is implemented withthe help of RSUs providing encryption mechanismfor all the vehicles that are registered with thesystem. An authentication process is employed by thecentralized system for the purpose of validating aswell as issuing certificates to registered vehicles. Sourcevehicles are issued encrypted certificates during thetransmission of information, while, these certificatesare decrypted by providing a public key to destinationvehicles. In addition to this, unique encrypted digitalsignature generated by the source vehicle and attachedto a Pinf o facilitates in identifying changes in theoriginal Pinf o by a destination or relay vehicles. Anychange in the original Pinf o causes the centralizedsystem to either not issue or validate attachedencrypted certificate. The process introduced in thisstudy establish an authentication process withoutcompromising anonymity. However, the process is notapplicable in environments lacking RSUs as it is heavilydependent on a centralized system implementedthrough RSUs. Moreover, public nature of informationin broadcasting would increase the complexity of theoverall system due to repeated requests for issuing orvalidation of certification for authentication.In [6], authentication process based on encryptedvehicle signature is used to establish authenticationbetween a vehicle and an RSU. After successfulauthentication, RSU issue a short-lived anonymouscertificate to the vehicle. This certificated as well aspublic key and signature are broadcasted by the vehicleto all the neighboring vehicles. The broadcasted Pinf o isverified by all the neighboring vehicles with the RSU.Source vehicle in this scenario transmits encryptedPinf o, which is decrypted using public key providedby vehicle to its neighbor. This secure system preventsexternal attacks by employing encrypting transmittingPinf o as well as registration of vehicles with RSU.However, the system is dependent on the availability ofRSU and lack a mechanism to identify internal attacks.Encryption mechanisms used for vehicle authenticationas well as encryption purposes play a vital role increating secure P2P systems. Both these mechanismshelp to establish P2P systems that are robust enough

such that they are available to the users even undermalicious attacks. For interested readers, a detailedlist of literature describing such secure and robustsystems based on encryption mechanisms is availableat [7–10, 20]. In addition to this, anonymity inP2P communication facilitates in securing confidentialinformation of vehicles such as speed, identity, andlocation of vehicles. The methodologies used foranonymizing vehicle information in literature ofP2P VANETs are based on either pseudonyms ofk-anonymity principles [6–13]. In the pseudonymapproach, a vehicle is allotted an alias from a pool ofpseudonyms by using a different algorithm to achievevehicle anonymity. On the other hand in k-anonymityapproach, vehicle information attributes are eithersuppressed or generalized to avoid identification andtracking of a vehicle and its passengers.

2.2. Security in Broadcasting (BC) CommunicationIn the BC, the information is shared among all vehiclesin the network, therefore this information is classifiedas public. Security aspects are relatively new in theVANET broadcasting, consequently the research paper[21] is the only research paper we were able to find.In [21], a detail and analytical discussion related tosecurity perspective of the multi-hop broadcasting mes-sage is discussed. The paper identifies and providespossible solutions based on the previous research stud-ies in other wireless networks. A novel methodologyor technique has not been proposed in this paper. Tothe best of our knowledge, there has been no othernovel methodology or technique being proposed duringthe writing process of this paper. On the other hand,the three distinct security parameters of authentication,anonymity, and availability of resource remain equallyimportant for the security of broadcasting. Therefore,we can extend the strategies available in P2P VANET tothe security applications in BC.The concepts and associated principles required for theauthentication mechanisms explored in P2P commu-nication are implementable for BC as well. Whereas,anonymity techniques based on either pseudonyms ork-anonymity principles are also effective in case ofBC. However, due to public nature of information inBC, encryption and cryptographic techniques used forencryption of the original Pinf o cannot be applied intheir current form.

3. Generalized VANET System ModelIn this section, we present a general purpose VANETsystem model with v = 1, ..., V vehicles in the network.These vehicles move with speed, s, of 60 to 100 km/h inthe same direction on a highway that consists of multi-ple lanes. On the other hand, the vehicles on the urbanenvironment travel with the same speed, however these

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Figure 1. Layered architecture of the proposed secure broadcasting in the VANETs

Figure 2. Operating modes of the proposed secure broadcasting architecture

vehicles are able to run left or right depending on theavailability of the road. Moreover, the vehicles are ran-domly distributed capable of communicating with eachother using the IEEE 802.11p communication protocol.The IEEE 802.11p belongs to the family of the IEEE

802.11 wireless protocol standards created to supportmobile vehicular communication networks [22, 23].Due to the availability of a large number of features inthe IEEE802.11p, it has become the de facto protocolfor VANETs [24]. Among these features, Carrier Sense

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Secure Communication in VANET Broadcasting

Multiple Access with Collision Avoidance (CSMA/CA)and beaconing system are the two vital features thatplay important part in our research [25].The CSMA/CA is a packet collision avoidance pro-cess that facilitates in the seamless transmission ofinformation in a network. In this process, a vehicle,which has a desire to transmit, is required to sensethe network for the purpose of establishing networkusage. An immediate transmission will proceed whenthere is no other transmission by any other vehicle inthe network. However, a random wait time, formallyknown as contention window, is assigned to the vehicleif the network is busy. After expiry of this wait time,the vehicle will check the network again and dependingon the status of the network, the vehicle will eithertransmit or assign another wait time. The process ofassigning wait time will continue until informationis transmitted. Presence of the CSMA/CA helps toavoid implementation of complex collision avoidanceand detection system, which would have increased thecomplexity of our system many folds.Beaconing system is another feature of the IEEE802.11p that helps a vehicle to maintain an up to dateinformation regarding their neighborhood This infor-mation facilitates accurate calculation of the probabilityof neighborhood, Pnc, which is vital in calculating waittime, WT , of an Pinf o. Pnc, WT and other variablesof the retransmission system are further discussed inSection 4.

4. Proposed Secure Broadcasting Architecture

A layer based secure broadcasting architecture has beenproposed in this Section. The purpose of this proposedarchitecture is to identify any type of alteration in pub-lic information during BC. The proposed architectureconsists of five different layers, namely anonymity, cred-ibility, encryption/decryption, relay vehicle selectionmethod, and transmission layer as shown in figure 1. Inaddition to this, these layers support different operatingmode discussed in Section 5. A detailed discussionrelated to functionalities associated with these layers isexplained in the following subsections:

4.1. Anonymity Layer (AL)

Anonymity layer (AL) facilitates in anonymizinginformation for the purpose of hiding identifiableinformation of a vehicle. Techniques, such as sharedpseudonym pool, put forward in Section 2 for P2P canbe introduced in anonymity layer to anonymize vehicleinformation. In this technique, each network in VANETshas a shared pseudonym pool consisting of unique aliasthat can be chosen by a vehicle to shield its identity.

4.2. Encryption/Decryption Layer (EDL)Encryption is one of the most effective and efficientsystems to secure information. Therefore, we proposean encryption/decryption layer (EDL) to achieve thisfunctionality in our model. This layer can be used toencryption actual information as well as the signatureof vehicles to preserve the authenticity of a Pinf o. Dueto public nature of Pinf o, the encryption strategiesavailable in P2P discussed in Section 2, such as [8–10],are not directly applicable in BC.

4.3. Relay Vehicle Selection Method (RVSM) LayerRVSM layer is required during the transmissionphase for the purpose of avoiding the broadcastingstorm. The broadcasting storm is caused by blindretransmissions to achieve network coverage, which isa process of achieving propagation of Pinf o, to all thevehicles in a network. The RVSM layer consists of atechnique, put forward in previous research [24], thatassigns a wait time, WT , based on the probability ofneighborhood coverage, Pnc, to avoid the broadcastingstorm. A Pinf o is broadcasted after the assigned WThas expired. The probability of neighborhood coverage,Pnc, is determined by all the vehicles, Nnp, thathave received this information, and all the vehiclesin the neighborhood database, Nvh, of that vehicle.Mathematically, Pnc can be defined as follows:

Pnc =

0, if Nnp= 01, if Nvh = 0NnpNvh

, otherwise .

(1)

4.4. Creditability Layer (CL)Credibility layer establishes the authenticity of an infor-mation packet, Pinf o, which facilitates in the processof prioritization during transmission. The process ofestablishing authenticity for a vehicle consists of com-puting and storing historical information related tocredibility index, ∝, broadcasting probability, PBC , aswell as authenticated packet score, Pscore, of all thevehicles in its neighborhood. The credibility of a vehicleis defined by ∝ using historical data consisting of PBC ofall the previous retransmissions. Mathematically, ∝ isdefined as follows:

∝:=

1, if Bn= 01Bn

(∑Bni=1(PBC)i), otherwise ,

(2)

where Bn is the total number of historical retransmis-sions. In addition to this, a priority value is assigned tothe Pinf o using PBC using Algorithm 1. The PBC relieson a combination of ∝ and Pscore, which consists of anaverage number of authentic Pinf o received from the

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Source Vehicle

Transmission mode

Anonymity Layer

Encryption / Decription Layer

Neighbouring Vehicle

Recieving mode

Encryption / Decription Layer

Credibility Layer

Retransmission mode

Anonymity Layer

Encryption / Decription Layer

Transmit

RVSM

CalculateCredability Index

Brodcasting Probability

Historical Data

StoringCredability Index

Credibility Index

Historical Data

CalculationWait Time

Has Wait Time Expire?

Credibility Layer

Yes

CalculateBroadcasting

Probability

Packet AuthenticationHistorical Data

Credibility Index

Historical Data

No

StoringBroadcasting

Probability

Brodcasting Probability

Historical Data

Assign Broadcasting

Probabaility as Priority Index

Is there no higher

priority packet?

Yes

No

RVSM

CalculationWait Time

Has Wait Time Expire?

Yes

Figure 3. Detail explanation of different layers and transmission modes of the proposed secure broadcasting architecture

source vehicle. Formally, PBC is defined as follows:

PBC :=∝Pn

( Pn∑i=1

(Pscore)i

), (3)

where Pscore ranges between 1 and 0, while Pn arethe total number of packets received from the sourcevehicle. It is important to note that PBC of Pinf o may

increase or decrease if another vehicle in the samevicinity either confirms or contradicts the originalPinf o by the source. On the other hand, if a rebuttalis transmitted by source or any other vehicle in thevicinity, the Pscore transmitted by relay vehicle isdecreased by 0.1.

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Algorithm 1 Pseudocode of CreditGetPriority functionof Credibility Layer

1: function CL_GetPriority(Vid ,P idinf o,Pscore,isStore)2: if isStore then3: UpdateVehicleHistoricalData(Vid , Pscore)4: end if5: Array_Pscore ← GetVehicleHistoricalData(Vid)6: PN ← Length_of _Array_Pscore7: T otal_Pscore ← 08: for i ← 0 to PN do9: T otal_Pscore ← T otal_Pscore + Array_Pscore[i]

10: end for11: PBC ← random(T otal_Pscore/PN , 2)12: if isStore then13: UpdateBCHistoricalData(Vid , P

idinf o, PBC)

14: end if15: Array_PBC ← GetBCHistoricalData(Vid , P

idinf o)

16: BN ← Length_of _Array_PBC17: if BN = 0 then18: return [1, 1]19: end if20: T otal_PBC ← 021: for i ← 0 to BN do22: T otal_PBC ← T otal_PBC + Array_PBC[i]23: end for24: ∝← random(T otal_PBC /BN , 2)25: return [ ∝ ×10, total_Pscore]26: end function

4.5. Transmission Layer (TL)Transmission layer facilitates in the propagation ofPinf o in a communication network. The IEEE 802.11pprotocol governs the transmission of Pinf o over awireless medium, however, the transmission can alsouse other established protocols such as Wireless Accessin Vehicular Environment (WAVE). We assume that avehicle, v, transmits its information as a vector ~x suchthat:

~x = [x1, x2, ...., xn]1×N , (4)

where x1, x2, ...., xn are the coded information alphabets.The transmission vector, ~x, is affected by the wirelesschannel fluctuations, modeled by the channel matrix,H, and the noise vector, ~n. The information signalreceived on a vehicle, v, can be represented by ~yv andis given as:

~yv = H~x> + ~n, (5)

such that [~yv]N×1, [H]N×N , [~n]N×1 and ~x> representstranspose of ~x. We further assume that each elementof ~H is modeled as a Gaussian random variable andthe noise ~n is also modeled as uniformly distributedAdditive White Gaussian Noise, AWGN , with zero

mean and unit variance. Such a model is used in most ofthe VANET communication scenarios such as [26–28].Furthermore, the data rate at which each vehicle cantransmit the packets is denoted by rv and can be givenas:

rv = η log2

(1 +

Pt |HH∗|2

|~n|2

)bps, (6)

where Pt is the transmitted power, η is the bandwidthin Hz and (.)∗ denotes the complex conjugate transposeof a matrix.

5. Secure Broadcasting Operating Modes

The proposed secure broadcasting architecture consistsof three different operating modes, known as transmis-sion, receiving and retransmission modes. These modesoperate by utilizing secure broadcasting layers, whichare stacked together in different formation according tooperating modes shown in figure 2. These modes arefurther discussed in the following sections:

5.1. Transmission Mode

Algorithm 2 Pseudocode of Transmission Mode

1: function TransmissionMode(Data,Vinf o)2: WT ← 03: isT ransmit ← False4: Data[Pscore]← 15: while isT ransmit = False do6: ifWT = 0 then7: isT ransmit ← Check_CSMA_CS(Vinf o)8: WT ← RSVM()9: end if

10: WT ← WT − 111: end while12: VAD ← AL(Vinf o)13: Pinf o ← EDL(VAD , Data)14: Transmit(Pinf o)15: end function

A vehicle, known as source vehicle, is in transmissionmode during the process of transmitting an originalPinf o. The transmission mode requires a combinationof AL, EDL, and TL. AL anonymizes source vehicleinformation, while, EDL helps in encrypting vehiclesignature and other metadata. The encrypted informa-tion helps a vehicle to identify any message(s) that arecirculated with its encryption. The vehicle may identifyspam messages and broadcast a rebuttal to that messageif needed. This helps to safeguard the network againstspam messages and spamming vehicles. Pseudocode oftransmission mode is put forward in Algorithm 2.

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Algorithm 3 Pseudocode of Receiving Mode

1: function ReceivingMode(Pinf o)2: [Vinf o, Data]← EDL(Pinf o)3: CL_GetPriority(V idInf o, Data[id], Data[Pscore], T rue)4: end function

5.2. Receiving ModeIn receiving mode, a vehicle receives an original orretransmitted Pinf o. This mode consists of EDL and CL.The decryption part of EDL is used to decrypt receivedPinf o. The part of the message that is of public naturecan be decrypted by this layer. In addition to this, theCL comes after EDL. During receiving mode, the CLcomputes and updates credibility index of transmittingvehicle based on Eq.2. The Pseudocode of receivingmode is put forward in Algorithm 3.

5.3. Retransmission Mode

Algorithm 4 Pseudocode of Retransmission Mode

1: function RetransmissionMode(Data,Vinf o)2: [P riority, Data[Pscore]]←

CL_GetPriority(V IInf o, Data[I], Data[Pscore], False)3: WT ← 04: isT ransmit ← False5: while isT ransmit = False do6: ifWT = 0 then7: isT ransmit ←

Check_CSMA_CS(Vinf o, P riority)8: WT ← RSVM()9: end if

10: WT ← WT − 111: end while12: VAD ← AL(Vinf o)13: Pinf o ← EDL(VAD , Data)14: Transmit(Pinf o)15: end function

A vehicle is in retransmission mode when it decidesto retransmit an original or retransmitted Pinf o.However, before a vehicle decides to retransmit, it hasto go through an independent method run by all thevehicles in a network to establish their suitability toretransmit a message using RVSM layer. The RVSMlayer provides a WT to all the Pinf o that needs tobe transmitted. The transmission of a Pinf o proceedswhen WT assigned to it is expired. The CL is involvedafter the RVSM layer for the purpose of computingPBC . This probability facilitates in prioritizing all theinformation packets for the purpose of broadcasting.The Pinf o with the highest PBC is then forwarded to thetransmission layer for broadcasting over the wireless

Table 1. Simulation parameters

Parameters ValuesSimulation Area VariableFrequency 5.9 GHzType of Road Highway with multiple lanesVehicle Densities 5, 10, 20, 40, 50,

100, 150, 200, 250,300, 350, 400, 450, 500 vehicles

s Between 60 and 100 km/hProtocol IEEE 802.11pTransmission Range 1000m [29]

Table 2. Symbols and notations

Symbol DescriptionPinf o Information PacketNR Number of RetransmissionsWT Wait TimeT T L Time To LivePNC Probability of Neighborhood CoverageNNP Number of vehicles that have received

the transmitted packetNVH Number of neighboring vehicles in

the neighborhood.V Total Number of vehicless Speed of vehiclesPscore PacketScorePN Total Number of Packet recievedPBC Probability of Broadcast CommunicationBN Total Number of BNVinf o Vehicle Information DatasetVid Vehicle IdentityV idinf o Vehicle Identity Property from

Vehicle Information DatasetP idinf o Information Identity Property from

Pinf o Dataset∝ Credibility Index

medium. The Pseudocode of receiving mode is putforward in Algorithm 4.

6. Results and AnalysisThe secure broadcasting architecture is implementedusing a real-time simulation model of highway andurban environments consisting of a priority queuemodel. The real-time simulation model is developed inPython are conducted on supercomputer Raijin, locatedin Canberra, Australia [30]. The machine is equippedwith state-of-art Fujitsu high-performance processorand has distributed memory cluster that facilitatedin achieving overall lower simulation complexity.Multi and parallel processing is supported by the

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100 200 300 400 5000

2,000

4,000

6,000

8,000

Vehicles

Ave

rage

netw

ork

cove

rage

tim

e(m

s)

Non-secure HighwayPBC = 1PBC = 0.8PBC = 0.6PBC = 0.4PBC = 0.2PBC = 0

Figure 4. Average network coverage time for different PBCscenarios in vehicular mobile environments for various vehicledensities.

100 200 300 400 500

200

400

600

Vehicles

aver

age

num

ber

ofre

tran

smis

sion

s

Non-secure HighwayPBC = 1PBC = 0.8PBC = 0.6PBC = 0.4PBC = 0.2PBC = 0

Figure 5. Average number of retransmission in for different PBCscenarios in vehicular mobile environments for varied densities.

supercomputer, which is based on Unix system.Moreover, prioritization of Pinf o in the priority queueis based on Time-To-Live (TTL) and PBC . A Pinf owith a higher value of TTL decreases its priority ofretransmission as compared to the lower value of TTL,on the other hand, higher values of PBC increasestransmission priority of the Pinf o. The results relatedto the effect of PBC on network coverage time and thenumber of transmissions is compared with an unsecurehighway and urban environments. The highway andurban scenarios categorized as unsecure lack PBC toestablish priority of the Pinf o. In addition to this, thesimulation parameters are put forward in Table 1, whileTable 2 contains symbols and notations used in thispaper.

100 200 300 400 5000

2,000

4,000

6,000

Vehicles

Ave

rage

netw

ork

cove

rage

tim

e(m

s)

Non-secure UrbanPBC = 1PBC = 0.8PBC = 0.6PBC = 0.4PBC = 0.2PBC = 0

Figure 6. Average network coverage time for different PBCscenarios in vehicular mobile environments for various vehicledensities.

100 200 300 400 500

200

400

600

Vehicles

aver

age

num

ber

ofre

tran

smis

sion

s

Non-secure HighwayPBC = 1PBC = 0.8PBC = 0.6PBC = 0.4PBC = 0.2PBC = 0

Figure 7. Average number of retransmission in for different PBCscenarios in vehicular mobile environments for varied densities.

Additionally, there are different experiment conductedto verify our proposed secure broadcasting architecturediscuss concepts discussed in the paper above. Thevehicle densities vary between 5 and 500 vehiclestravelling on either highway or urban scenarios. Inaddition to this, vehicles also maintain a safety distanceof 70 to 120 meters. The highway scenario consists of 3lanes and vehicles on highway travel in one direction.On the other hand, there are six roads containing twolanes to allow opposite travel of vehicles in an urbanscenario. These roads connect to each other at differentpoints enabling vehicles to turn left or right. In additionto this, the results of the experiments consists of exactly50 Pinof having values of PBC ranging from 1 to 0.Another important parameter is the number of Pinof

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0 0.2 0.4 0.6 0.8 1

200

400

600

800

1,000

1,200 Point A(0.20,1058)

Point B(0.90,220)

Broadcasting probability (PBC)

Net

wor

kC

over

age

Tim

e(m

s)

Propagation Time (ms)

Figure 8. Average number of retransmissions in for differentbroadcasting probability ,PBC , scenarios in vehicular mobileenvironments for varied densities.

available for broadcasting at a certain time. In oursimulations, the results indicated no significant effecton the experiments for less than 50 Pinof in the network.In addition to this, the result show very closely numbersfor non-secure and PBC score of 0, therefore the non-secure highway as well as urban scenarios are hiddenbehind PBC results of 0. The experiments are furtherdiscussed in following two subsections:

6.1. Network Coverage Time

In the first experiment, we investigate networkcoverage time, which is defined as a time required forpropagation of a Pinf o to all the vehicles in the network.The Pinf o that consists of lower values of the PBC aretransmitted after those Pinf o with higher values of PBCare transmitted. Therefore, network coverage time ofa PBC is directly proportional to the number of Pinf owith higher PBC and vehicle density. The effects ofchange in network coverage time with respect to thenumber of Pinf o with different PBC can be observed infigures 4 and 6 for both highway and urban scenariosrespectively. The Pinf o network coverage time increaseswith the decrease of PBC , whereas, an increase invehicle density also increases network coverage time.In addition to this, an increase in network coveragetime due to vehicle density is caused by the increasein the number of vehicles needed to receive Pinf o in anetwork. On the other hand, network coverage time isquite consistent for the non-secure highway as well asurban environment.

Table 3. Transmission information and broadcasting over time

T ime V rid V tid P idinf o ∝ Pnc

t40

V22V18 2 0.3 0.3V20 1 1 0.3

V23V19 5 0.9 0.3V14 6 0.6 0.3

V24V17 8 0.1 0.3V16 9 0.2 0.3

t41

V22 V18 2 0.3 0.3

V23

V22 1 1 0.7V19 5 0.9 0.3V14 6 0.6 0.3

V24

V22 1 1 1V17 8 0.1 0.3V16 9 0.2 0.3

6.2. Number of RetransmissionIn the second experiment, we explore the number ofretransmissions exhibited by the secure broadcastingarchitecture for both highway and urban scenarios. Theexperiments for each vehicle density are repeated atleast ten times. The number of retransmissions, NR,is directly proportional to the distribution of vehiclesrather than delay in transmission. Therefore, NR shouldexhibit nearly the same values irrespective of the PBC .However, delay in transmission may cause changes inthe distribution of vehicles due to the movement ofvehicles over time. That is one of the reasons for thedifferent number of average retransmissions observedin figure 5 and 7 for different Pinf o irrespective of theirPBC .

6.3. Network Coverage Over TimeIn the last experiment consisting of results depictedin Figure 8, we present network coverage over time ina network comprised of 100 vehicles. At point A inthe figure, a PBC of 0.2 requires an average of 1058ms to achieve network coverage, while a PBC of 0.9requires an average network coverage time of 220 msat Point B. These results show around 80% decreasein the network coverage, when moving from 0.2 to0.9 PBC . Therefore, it can be deduced that the networkcoverage time increase with the decrease of PB as wellas observing of similar tendencies of results comparedto the previous discussions regarding the increase inthe number of retransmissions and network coveragetime. In addition to this, the analysis with respect todifferences and similarities of the results produced byhighway and urban scenario is put forward in [24].

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Secure Communication in VANET Broadcasting

Figure 9. Broadcasting of different packets with different priorities in a network

6.4. Simulation AnalysisIn Table 3, a simulation snapshot is present to provideanalyses related to the impact of ∝ in the transmissionprocess. At the beginning of the simulation, the vehiclein the network does not have enough number of thePinf o so that the decision of transmitting the Pinf o canbe made. In order to present the explanatory numericalresults, we start from the vehicle V rid = V22. However,the starting vehicle can be any other vehicle in thenetwork. The neighborhood of the V22 is depicted inthe table, which consists of vehicle 23 and 24. At a timeinterval t40, the table shows each vehicle containingdifferent Pinf o identified by their identity property,P idinf o. Each of the Pinf o have different ∝ and duringtransmission, the broadcasting system assigns lowerWT to highest ∝ in the neighborhood. At t40, the P idinf o 1of vehicle 22 is allowed to be broadcasting since its ∝ ishighest in the neighborhood. On the other hand, At t41,the P idinf o 1 of vehicle 23 is allowed to be broadcasting,and the same Pinf o is not allowed to broadcast forvehicle 24 due to fact Pnc is 1. The 1 value of Pnc isachieved when all the neighbors of the vehicle receiveda Pinf o, therefore there is no need to broadcast this Pinf o.

A similar scenario related to prioritized transmissionsof Pinf o in a system is show in figure 9.

7. ConclusionIn this paper, we have identified and categorized secu-rity challenges related to broadcasting in VANETs. Tocounter these security challenges, a secure broadcastingarchitecture was proposed for the purpose of securingpublic information from intruders. The secure broad-casting architecture is layered based architecture whichis stacked together in different formation accordingto operating modes. The network computer facilityconsists of supercomputer having a real-time simula-tor designed in Python was used for the purpose ofcollecting results. These results show an increase innetwork coverage time to achieve network coveragewithout having any significant differences in numberretransmissions when compare with unsecure highwayor urban scenarios. The future work of this study is toextend this model to include dynamic readjustment ofcredibility index and broadcasting probability over thenumber of time intervals for further verification of theproposed architecture.

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