A Secure Wireless Communication Scheme for Vehicle ad hoc Networking Paper by: . Ching -Hung Yeh

1. DESCV A Secure Wireless Communication Scheme for Vehicle ad hoc Networking Paper by: .Ching-Hung Yeh . Yueh-Min Huang .TzoneIWang .Hsiao-Hwa Chen Presented by:Dipti KothariRegina CherianNavyaPothineni Dynamic Establishment of Secure Communications in VANET

2. Introduction • Inter Vehicle Communication is an important part of VANET(Vehicular ad-hoc Networking) . • Basically provides communication between vehicles. • How to provide inter vehicle communication? • Centralized Infrastructure Key Management not possible due to mobile vehicles and ad hoc links. • Road Side Units (RSU) Not Feasible to fix RSU on all the roads round the world.

3. The paper deals with Decentralized IVC without fixed infrastructure. • Dynamic Establishment of Secure Communications in VANET (DESCV), aims at providing random vehicle-to-vehicle secure wireless connections. • Vehicles can quickly establish their encrypting keys when they need to communicate with each other. • Its operation does not depend on any centralized infrastructure • Due to increasing number of vehicles, IVC has become challenging. • Through wireless transmission interfaces, cars exchange messages which is collected in On Board Unit(OBU).

4. Factors effecting IVC • There are 2 important factors in IVC • Safety • Comfort • Safety Includes emergency warning systems and anti collision system. • Comfort Includes traffic conditions, gas stations, restaurant locations and their price differentiation. Secure message delivery for both safety and comfort is important as it will affect navigation plans and response time to any upcoming emergency or accident.

5. Security in IVC For security of IVC, We would use Cryptography and would consider 4 parameters • Authentication - Incident responses should be based on correct authenticated messages. • Privacy – Messages must be protected against unauthorized entities. • Confidentiality – MIM should be avoided. • Non Repudiation- Vehicles causing accidents must be identified and false message sender should not deny his message.

6. The Techniques • Secure communication uses Cryptographic techniques. • Unfortunately, conventional PKI relies on centralized or hierarchical certificate authority to conduct key management which is not preferred in an environment where vehicles speed at a high rate. • Centralized Infrastructure Road Side Units

7. Why DESCV? • These security mechanisms may not be suitable to a VANET in which vehicles have free movement and may require ad hoc based wireless connections. • Extremely high cost required to deploy a sufficiently large number of RSUs . • Moreover, vehicles may travel through different cities, states and countries, where usually not all roads are covered by RSUs. • Pre-defined symmetric key schemes may not suit well for VANET because a vehicle normally has difficulties to predict to which vehicles it has to connect. • If the symmetric key has been disclosed, neither sender nor receiver can keep the secret.

8. Why not existing algorithms? • At first several algorithms were proposed. • Combined signatures, overlapping groups and dynamic group key creation were considered. • But the catch was to find a tradeoff between robustness in security and efficiency of the algorithms. • Our study in this paper is focused mainly on an ad hoc vehicle-to-vehicle network. (_without fixed infrastructure_) • Vehicles using DESCV can quickly establish the encrypting keys. • Also we do not need to disclose their decrypting keys to avoid malicious attacks.

9. The Algorithm Involves 3 steps Step 1: Initiate a super-increasing set A=(a1,a2,··· ,an), and two prime numbers, w and M, satisfy M > n∑i=1 a i Calculate θ which ensures w ∗ θ ≡ 1 (mod M). Step 2: Generate B=(b1,b2,··· ,bn) using bi ≡ ai∗w (mod M) where {bi|bi< M, i = 1,2,··· ,n} Transform B = (b1,b2,··· ,bn) into B´= (b´1,b´ 2,··· ,b´ n) by using b´≡ bi (mod w) where {b´i|b´i< w, i = 1,2,··· ,n} B´ can be used to generate E which is the encrypting key. It can be calculated as ei=bi if bi < P else ei =bi –k where P= (min b’i +max b’i)/2 and k is a random number less than P.

10. The Algorithm! Step 3: For decrypting purpose, calculate di = biw where 0 ≤ di≤ u, and generate decrypting Key A´ = (a´1,a´2,··· ,a´n), for all a´i= ai−di

11. Security • The bottom-line objective is that secure communications can be quickly established and the propagation of packets over wireless links is well protected. • Therefore, the exchange of the encrypting key is the primary goal. • Also it has to be noted that the ID is automatically retrieved from OBU. The packets are recognized by vehicles using the IDs. Key Management • Keys are generated each time a vehicle wants to interact with a new vehicle which results in an overhead in key management. • However, DESCV effectively removes the burden for key pre-storage and key distribution. • In DESCV, the encryption key E dynamically adapts a simple way of changing parameters

12. Security Analysis • DESCV is safe against passive attacks and active attacks. • Encrypting keys Ei’ and Ejare delivered confidentially. • Even if the adversary has the cipher text and knows the algorithm and request response packets , he would need P, k , M, θ and A’ for decrypting • The value of E depends on B’ which in turn depends on P and k. • The value of P in turn depends on B’ (P=(b’min+b’max)/2). • Thus P and B’ place constraint on each other forming a deadlock. • DESCV is safe from brute force attacks.The adversary need to calculate E= (e1, e2, · · · , en). • For n = 64 then the adversaries need to try 2^64 ≡ 10^19 calculations. • For solving this successfully it will need around 10^2.5 years which is sufficiently long to protect the information. • DESCV is safe from man in the middle attack.If the adversary attempts to impersonate an endpoint in the middle that will fail too because the ID is retrieved from OBU and protected by both encrypting keys Ejand ´Ei,

13. Throughput • VANET does not need high throughput to support its communications • Difference in throughput of vehicles adopting DESCV and without DESCV does not exceed 5kB/s

14. Evaluation and Conclusion • Inter Vehicle Communication cannot be successfully implemented through fixed architecture (RSU, Centralized infrastructure) because of continuous vehicle movement. • DESCV is inherently simple to implementand simulation results show that its operation takes into account both efficiency and security. • The main advantage is establishment of a secure encryption key for vehicle to vehicle communication that does not rely on any centralized infrastructure.

15. Questions???