Region Authority (RA) Collaborated Certificate Organization and Management in VANET

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1 Region Authority (RA) Collaborated Certificate Organization and Management in VANET Shahnawaj Khan CSE Department National Institute of Technology, Hamirpur Hamirpur, India Abstract- Vehicular ad hoc networks (VANETs) are receiving increasing attention from academics due to the various applications and potential tremendous benefits they offer for future VANET users. Safety information exchange enables lifecritical applications, such as the alerting functionality during medical emergencies, and thus, plays a key role in VANET applications. In a VANET, vehicles rely on the integrity of receiving data for deciding when to present alerts to drivers. The communication between car to car, car to the roadside unit done through wireless communication. That is why security is an important concern area for vehicular network application. For authentication purposes large amount of bandwidth is consumed and the performance becomes low. In VANET some serious network attacks such as man in the middle attack, masquerading is possible. In this paper various previous researches done in this area are analyzed and compared on the basis of drawbacks of those approaches. After that the different issues on VANET are discussed and finally conclude with proposed idea. Keywords-Security, Region authority (RA), on board unit (OBUs), certificate revocation lists (CRLs). I. INTRODUCTION Vehicular Ad-Hoc Network is a special class of Mobile Ad-Hoc Networks (MANETs) in which communication link is established between road side units (RSUs) and on board units (OBUs), OBUs to OBUs in a short range of 100 to 300 m and between RSUs to RSUs. To enable application for safety, traffic, driver assistance, infotainment vehicular communication is evolving very rapidly. But the race of providing various services raises the security concern and makes VANET vulnerable to various attacks like jamming, forgery, privacy violation, on board tampering. Existing protocols to secure VANETs resolves these issues up to some extent but raises some concerns on the basis of which, this paper reviews the different schemes developed for VANET. More specifically, the purpose of the paper is to survey the literature, and provide an overview of the extent of the research done in the area of VANETs and also provide some protocols to resolve the security issues. This paper is organized as follows: In the second section the challenges for the security in VANET are discussed. In the third section, previous work that is close to this approach has been discussed. In the fourth section, system model which we Naveen Chauhan CSE Department National Institute of Technology, Hamirpur Hamirpur, India naveenchauhan.nith@gmail.com assumed for the proposed scheme is discussed. In the fifth section, evaluation criteria are discussed based on which proposed scheme is evaluated. In section sixth proposed scheme is discussed. In section 7 paper is concluded. II. CHALLENGES The most significant challenges of VANET are A.Network Volatility The connectivity among nodes can often be highly transient and a one-time event (same vehicles may not get the chance to communicate again). For example, two vehicles (nodes) traveling on a highway may remain within their transceiver range, or within a few wireless hops, for a limited period of time. Hence password-based establishment of secure channels, gradual development of trust by enlarging a circle of trusted acquaintances, or secure communication only with a handful of endpoints and may be impractical for Securing vehicular communication (VC). B. Authentication vs. Privacy In the process of providing authentication for communication between OBUs, The privacy of the sender can be revealed and can pose threat to the sender by many ways like tracking someone s location, journey details. C. Delay Sensitive Applications Many of the safety and driver-assistance applications Pose strict deadlines for message delivery or are Time-sensitive. Security mechanisms must take these constraints into consideration and impose a low processing and messaging overhead. D. Network Scale The scale of the network, with roughly a billion vehicles around the globe, is another challenge. E. Heterogeneity The heterogeneity in VC technologies and the supported applications are additional challenges, especially taking into account the gradual deployment. With nodes possibly equipped with cellular transceivers, digital audio and Global Positioning System (GPS) but with the current standard architecture using the vehicular public key infrastructure (PKI)

2 and tamper proof device (TPD) and various protocols these problems are resolved up to some point. III. PREVIOUS WORK In VANETs, the primary security requirements are identified as entity authentication, message integrity, nonrepudiation, and privacy preservation. The PKI is the most viable technique to achieve these security requirements. In [6] author proposed TACKs for certificate organization and vehicle revocation in a VANET, which we consider to be the most relevant and closely related scheme to the work we propose in this paper. TACK adopts a hierarchy system architecture consisting of a central trusted authority and regional authorities (RAs) distributed all over the network. The authors adopted group signature where the trusted authority acts as the group manager and the vehicles act as the group members. Upon entering a new region, each vehicle must update its certificate from the RA dedicated for that region. The vehicle sends a request signed by its group key to the RA to update its certificate, the RA verifies the group signature of the vehicle and ensures that the vehicle is not in the current Revocation List (RL). After the RA authenticates the vehicle, it issues short lifetime region-based certificate. This certificate is valid only within the coverage range of the RA. It should be noted that TACK requires the RAs to wait for some time, e.g., 2 seconds, before sending the new certificate to the requesting vehicle. It restricts the vehicle to send messages to neighboring vehicles within this period, which makes TACK not suitable for the safety applications. Also, TACK requires the RAs to completely cover the network, otherwise, the TACK technique may not function properly. This requirement may not be feasible especially in the early deployment stages of VANETs. In [1] author considers the deployment stage of VANET and proposes 3 protocols revocation using tamper proof device (RTPD) which uses the tamper proof device (TPD) to revoke all the certificates of the malicious vehicle with the help of radio or FM to broadcast in case of vehicle is not in the range of road side units (RSUs), distributed revocation protocol (DRP) which uses group based revocation technique to revoke the certificate. In case if any vehicle is suspected of doing malicious activity by its neighbor and if then the numbers of neighbors are greater than a certain threshold then they inform it to the CA to remove its certificate. The last is revocation using compressed certificate revocation list (RCCRL) which uses the distribution of the only updated and compressed list. For privacy it proposes using a set of anonymous keys that change frequently. These keys are preloaded in the vehicle s TPD for a long duration. For authentication vehicles will sign each message with their private key and attach the corresponding certificate. To reduce the security overhead, it uses the approach of elliptic curve cryptography (ECC). In [2] author does not consider the deployment stage problem. It uses the RSU aided certificate revocation scheme in which RSU checks all passing vehicles for revoked certificates which are already stored at RSUs distributed by the CAs to the RSUs. If revoked certificate is found from any malicious vehicle it inform to all local vehicles about the revoked certificate by broadcasting it locally. This helps in reduction in the size of the CRL and high cost of the distribution of the CRL. It also considered revocation using tamper proof device (RTPD), DRP, RCCRL which reduce the size of the CRL. It follows group signature and identity based signature (GSIS) to preserve the privacy of the vehicle. In [3] author only focuses on the CRL size and its distribution. It divides the CRL into various parts uses network coding and erasure coding to reassemble complete CRL with few pieces. Using erasure coding, a node will simply send out the same pieces it received without making any changes. Using network coding, a node will generate linear combinations of all of the pieces currently possessed, requiring greater processing capability at every OBU. Erasure coding has less overhead, both in packet overhead carry the coding information, and in processing overhead to reconstruct the file. It uses vehicle to vehicle (V2V) communicate to forward pieces between vehicles. The Most Pieces Broadcast method creates a situation where only the node with the most number of CRL file pieces is selected to broadcast within a given radio broadcast range. In [4] author focuses on the issue of authentication and privacy. Here CA uses a pseudo random key generator (PRNG) to generate all the certificates of a single vehicle so that only CA can backtrack the detail of the source. CA generate all the certificates by selecting a random number "n" then generate all the certificates from it and send all the certificates to the corresponding vehicle and hold the random no to itself so that in case of need of detail of the sender only CA can back track the identity of the vehicle. It also uses the group certificate policy in which vehicles have a very large database of certificate up to each certificate is valid up to a very short time period to ensure a high level of privacy. In [5] author uses a new approach to accelerate the certificate validation procedure by adding 2 new attributes credibility and issued date. Credibility is the measure of the authenticity of a particular vehicle. If a vehicle is having high credibility then it is a more trust full vehicle and the other one shows the date at which the particular certificate has been issued. With k-mean clustering it divide CRL into the k- cluster. Each cluster is divided based on these two new attributes. Whenever a request arrives, to check its validity it is compared with the certificate resides in its cluster only which in term reduces the overhead to search the entire CRL. IV. SYSTEM MODEL As shown in Fig. 1, the system model under consideration consists of the following: A. Certificate Authority(CA) It is responsible for providing anonymous certificates and distributing secret keys to all RAs and OBUs in the network. It is assumed that it cannot be compromised.

3 B. Region Authorities (RAs) These are fixed units dedicated only one for a region. RAs are the middleware between CAs and RSUs. It is assumed that it cannot be compromised. C. Roadside Units (RSUs) RSUs are considered to be fixed and installed throughout the network. The RSUs can communicate securely with their RAs. It can be compromised because these lies near the road so attacker can easily reach to them. D. On Board Unit (OBUs) These are embedded in vehicles. OBUs can communicate either with other OBUs through V2V communications or with RSUs through vehicle to infrastructure (V2I) communications. These have the highest chances of being attacked. According to the WAVE standard, each OBU is equipped with a TPD, which is a tamper-resistant resistant module used to store the security materials, e.g., secret keys and certificates of the OBU. Also, the TPD in each OBU is responsible for performing all the cryptographic phic operations such as signing messages, verifying certificates, keys updating. We consider that legitimate OBUs cannot collude with the revoked OBUs as it is difficult for legitimate OBUs to extract their security materials from their TPDs. Finally, we consider that a compromised OBU is instantly detected by the RA. V. PROPOSED SCHEME In this approach the functionality of RAs and RSUs are very distinct as compare to the other scheme, we have seen so far. OBUs are loaded with certificates in its tamper proof devices (TPDs) by the certificate authorities (CA), which are valid for a long time. These are loaded with large numbers so that OBUs need to update only once in a year. Certificates are generated by the CA for each OBUs and only CA can recover the original identity of the OBUs. Algorithm 1 Certificate Generation Algorithm 1. M = no. of certificates per time interval for vehicle. 2. I = no. of time intervals during a reload period. 3. Begin 4. n = get random number() 5. for i = 1 to I do 6. S i = H i (n) 7. for j = 1 to M do 8. (PK j,i, SK j,i ) = generate public private key pair() 9. SIG CA,j,i = SIGN(H{E Si (j), PK j,i }), SK CA ) 10. CERT j,i = {E Si (j), PK j,i, SIG CA,j,i} 11. UPLOAD((CERT 1,i,PK1,i,SK1,i SK1,i)...,(CERT M,i, PKM,i, SKM,i)) at OBU 12. end for 13. end for 14. end Whenever the vehicle enters a new region, it needs to obtain the certificate for that region. With the help of road side units (RSUs) which are used only for communication purpose only in this approach because they are located near the road and highly vulnerable to attack.. RSUs here are used only to cover the entire network. Once RSU get any request for the certificate by a vehicle. It forwards it to the RA of its region. RA has two types of certificate revocation lists (CRLs). Revocation list of RSUs as well as the revocation list of the OBUs. Revocation list of the OBUs at RA is provided by the CA while the RL of RSUs is generated by RA itself by detecting any malicious activity by any RSU. On getting any request by any OBU it checks it against all the entries of the CRL for the OBUs. If no entry is found then it generate a temporary certificate, valid for a short time period and in that region only. These certificates are sent to the corresponding vehicle Fig.1. System model

4 along with the CRL of OBUs as well as RSUs of that region only. CRL is very small in size to distribute and search. CRL is also updated time to time on any revocation of certificate by distributing only required pieces of information. Algorithm 2 Certificate updation algorithm AT OBU 1. N = no. of possible regions in path. 2. Begin 3. for i = 1 to N do 4. X = SIGN SK (PK,CERT CA ) 5. SEND(X,PK,CERT CA ) to RA 6. end for 7. end AT RSU 1. Begin 2. verify(x,cert CA ) 3. (PK V, SK V, ) = generate public private key pair() 4. Y = SIGN SKRA (PK V, CERT CA ) 5. CERT RA = (Y, Expiration, RA id ) 6. add (X, CERT RA ) in history table of RA 7. SEND (CERT RA, PK V, SK V, RA id, CRL OBU, CRL RSU )to OBU 8. End A. Certificate Generation To upload certificates initially in an OBU, it requires a number of certificates for a time interval as well as the number of time intervals during a reload period. Here n is a random number, the S i is a key to some block of certificates. It is generated by hashing n by i times using some hash function 'H'. PK and SK are public and secret key pair. Signature is used to ensure integrity of the certificates by hashing the public key and encrypted value of 'j' using block identifier 'S' and then applying some signature algorithm with the secret key of CA. Certificates are generated by using sign, public key, and encrypted value. Now these are uploaded to the OBU. B. Certificate Updation N is the number of possible region a vehicle can enter. OBU send its request to each RA for their certificates by sending a sign of PK and certificate CERT issued by the CA using its SK. Now on receiving the request from an OBU each RA verifies its signature and then its certificate. If it is not found in CRL then generate new public-private key pair and sign OBU's public key and its CERT issued by a CA by its SK. now it generates a new regional certificate with sign, expiration period and its region authority id. It further adds the mapping detail in its history table and then sends the certificate of its region and ID of its region to the OBU. C. Certificate authentication and verification Each OBU need to authenticate to each other before the start of communication. Sender OBU initially broadcast its PK to all the other OBUs as well as RA. For authentication, sender OBU generate the signature by signing the message M by its SK Y = SIGN SK (M) And then send (Y,M,CERT RA ) to the receiving OBU. On receiving the above parameters receiving OBU needs to verify before to start the communication. First receiving OBU checks the validity of the sign Y, then check the CERT RA against all entries of the CRL. IF match found M is dropped else further communication will be established. In TACK [6] RA delay the around 2 min to process the request of OBUs which is not considerable by VANET applications. In this paper RA collaborated approach is proposed to resolve such issue. Each RA is connected with their neighbor RAs to reduce the delay in the process. Before entering a new region OBUs can be easily facilitated by the functionality of early request of the certificate. Hence OBUs can have the certificate of the region even before entering it. Sometime it may also be possible that at any point vehicle can have a choice to enter into more than one region but generally it is restricted to either two or three regions possibility. In such case vehicle gets the early certificate of each region and with few choices it cannot be an accountable waste of resources. It considers all the challenges and facts about the VANET. The Deployment stage problem is resolved by providing only one RA for each region. It also restricts the work of RSUs with covering the network only. It also provides the low cost deployment with most of the coverage. It also provides the authentication with RA certificate as well as group based key while preserving the privacy. With pseudonymous certificates and the hierarchy approached used here. Search and distribution of CRLs also cost very low because of very few entries in each CRL to deal with. VI. EVALUATION CRITERIA In this section we define a set of evaluation criteria which will help us in the comparison of the different schemes. Following is a list of the evaluation criteria used in the revocation schemes in VANETs. A. Deployment Stage of VANET The very first thing to consider is deployment stage because currently either VANET is an idea for most of the world or it is in the deployment stage. To fulfill the complete objective of secure VANET. Deployment stage must be considered because each protocol has their different performance in partial and full deployment of VANET. B. Size of Certificate Revocation List and its Distribution As the revocation of certificates takes place frequently. And the size of the VANET is very large with having millions of vehicles around the globe. The problem of distribution of

5 the certificate revocation list (CRL) costs very huge amount of time and bandwidth. And with such huge size of CRL it also needs huge storage AT on board units (OBUs) as well as high processing speed to search that huge CRL. C. Authentication vs. Privacy Although each proposed scheme provides different methods for authentication between vehicles as well as providing privacy for the sender but there is a need to evaluate the performance of each protocol to ensure a high level of authentication while providing complete privacy in which only higher authorities can have the right to access the detail of the sender under any case of malicious activity. VII. CONCLUSION This paper proposes RAs based certificate organization and management scheme which resolves the basic challenges of VANET and provide a feasible solution of the deployment of VANET, The huge size of CRLs and its distribution and search, authentication and privacy. In comparisons with the available protocols, it can be deduced that the RA collaboration scheme will give better results than the existing ones. As the next step towards our research, we would like to augment this research with mathematical analysis and simulation result. REFERENCES [1] M Raya, P Papadimitratos and JP Hubaux, Securing Vehicular Communications, IEEE Wireless Communications, vol. 13, no. 5, pp. 8-15, October [2] X. Lin, R. Lu, C. Zhang, H. Zhu, P. Ho and X. Shen, Security in Vehicular Ad Hoc Networks, IEEE Communications Magazine, vol. 46, no. 4, pp , April [3] Michael E. Nowatkowski and Henry L. Owen, Certificate Revocation List Distribution in VANETs Using Most Pieces Broadcast, proceedings of the IEEE SoutheastCon, pp , [4] Jason J. Haas, Yih-Chun Hu, and Kenneth P. Laberteaux, Efficient Certificate Revocation List Organization and Distribution, IEEE Journal on Selected Areas In Communications, vol. 29, no. 3, pp , March [5] Qingwei Zhang, Mohammed Almulla, Yonglin Ren and Azzedine Boukerche, An Efficient Certificate Revocation Validation Scheme with k-means Clustering for Vehicular Ad hoc Networks, IEEE Symposium on Computers and Communications (ISCC), pp , [6] Ahren Studer, Elaine Shi, Fan Bai and Adrian Perrig, TACKing Together Efficient Authentication, Revocation, and Privacy in VANETs, 6 th Annual IEEE Communications Society Conference on Sensor, Mesh and Ad-Hoc Communications and Networks, pp. 1-9, 2009 [7] Albert Wasef and Xuemin Shen, EMAP: Expedite Message Authentication Protocol for Vehicular Ad Hoc Networks, IEEE Transactions on Mobile Computing, vol. 12, no. 1, pp , January [8] Vighnesh N V, N Kavita, Shalini R. Urs and Srinivas Sampalli, A Novel Sender Authentication Scheme Based on Hash Chain for Vehicular Ad-Hoc Networks, IEEE Symposium on Wireless Technology and Applications (ISWTA), pp , September [9] Hind AI Falasi and Ezedin Barka, Revocation in VANETs: A Survey, IEEE International Conference on Innovations in Information Technology (IIT), pp , [10] Albert Wasef, R. Lu, X. Lin and X. Shen, Complementing Public Key Infrastructure to Secure Vehicular Ad Hoc Networks, IEEE Wireless Communications, vol. 17, no. 5, pp , October [11] Ghassan Samara, Wafaa A.H. Al-Salihy and R. Sures, Security Analysis of Vehicular Ad Hoc Networks (VANET), Second International Conference on Network Applications Protocols and Services (NETAPPS), pp , [12] Nurain Izzati Shuhaimi and Tutun Juhana, Security in Vehicular Ad-Hoc Network with Identity-Based Cryptography Approach: A Survey, IEEE 7th International Conference on Telecommunication Systems, Services, and Applications (TSSA), pp , 2012.