Secure pseudonym generation for efficient broadcast authentication in VANETs Deepak N Ananth and Manjusha Gadiraju CSC / ECE 774

Broadcast Authentication in VANETs  Outline:  Introduction to VANET Technology  Security requirements in VANET technology  Privacy protection in VANET  The proposed Protocol  Fast Authentication in VANET  Implementation and Future Work  References 2

Why VANET? - Motivation  Increase traveler safety  10.8 million vehicle crashes from 1990 to 2009  36,000 fatalities in 2009 only  24,000 of these due to collision with other vehicles / objects.  Costs more than $100 billion per year  Boost on-board luxury 3 Source: US Census Bureau :

Broadcast Authentication in VANETs  Outline:  Introduction to VANET Technology  Security requirements in VANET technology  Privacy protection in VANET  The proposed Protocol  Fast Authentication in VANET  Implementation and Future Work  References 4

What is Vehicular Ad-Hoc Network ? 5 Higher Authority RSU m :, loc, Tv S(m) : ECDSA signature cert : Public key certificate m :, loc, Tv S(m) : ECDSA signature cert : Public key certificate OBU

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Communication in VANET 7 Vehicular communication Vehicular communication Vehicle-Vehicle Vehicle-Infrastructure Single-hop Multi-hop Hybrid

VANET Applications Co-operative Collision WarningLane Change WarningIntersection Collision Warning Approaching Emergency vehicleRollover WarningWork Zone Warning Coupling/DecouplingInter-Vehicle CommunicationsElectronic Toll Collection 8

VANET Characteristics  The main characteristics of VANETs  High mobility of nodes  Rapidly changing network topology (predictable to some extent)  Unbounded network size  Potential support from infrastructure  Real time, time-sensitive data exchange  Crucial effect of security and privacy 9

Broadcast Authentication in VANETs  Outline:  Introduction to VANET Technology  Security in VANET technology  Privacy protection in VANET  The proposed Protocol  Broadcast Authentication in VANET  References 10

Security Requirements  Authentication  Privacy protection  Non-repudiation  Real-time constraints  Availability 11

12 Security Requirements (contd)

 Outline  Introduction to VANET Technology  Security requirements in VANET technology  Privacy protection in VANET  The Proposed Protocol  Fast Authentication in VANET  Security Analysis  Implementation and Future Work  References 13

Privacy – Important for VANETs  Cars = Personal Devices  Tracking of vehicles based on communication messages  The feeling of permanently being monitored by an arbitrary authority

Examples: Privacy threat  A private investigator can easily follow a car without being noticed by extracting position information from the messages sent by the car.  An employer is overhearing the communications from cars on the company parking lot.

How to provide Privacy ???  Enter “pseudonyms” aliases which hide the real identity  Can be implemented using random numbers  Set of pseudonyms used during communication must be mapped to real-world identities in special situations Trusted Authority

How to use pseudonyms?  Single pseudonym all the time –Easy to map alias with real identity –Messages can be related  Store pseudonyms on the OBU and use over a long period of time –How many pseudonyms to load ? –Compromised node ?

Broadcast Authentication in VANETs  Outline  Introduction to VANET Technology  Security requirements in VANET technology  Privacy protection in VANET  The Proposed Protocol  Fast Authentication in VANET  Security Analysis  Implementation and Future Work  References

Protocol Overview  Privacy protection for local broadcast messages.  Short time on-the-fly pseudonym generation.  Estimate the number of pseudonyms required.  Local broadcast via Enhanced Fast Authentication

System Model

System Components  Central Authority (CA) : Centralized authority which registers the vehicles before they are allowed to operate on the road. E.g.: DMV Cannot be compromised  Roadside Authority (RA) : Authorized all road-side units. Cannot be compromised.  Road Side Units (RSU) : Infrastructure nodes installed Road side. Susceptible to compromise  Vehicular nodes: Nodes which transmit the messages. Susceptible to compromise

Assumption Model  Each vehicle V when registered with the CA is provided a public / private key pair and CA pub  The RA periodically pulls information from the CA to get the latest up to date CRL’s and registered vehicles information.  Each RA maintains a topological overview of the entire area under its coverage  Attacker can compromise at most one RSU under a RA’s range.  At any time in the network there are more number of benign nodes than the compromised nodes.

Attacker Model  External Attacker: Such an attacker is limited in the diversity of attacks he can mount. However, he can eavesdrop on all the messages transferred.  Inside Attacker: The attacker can be an authenticated member of the network; such an attacker can communicate with other members of the network. E.g: Compromised RSUs and vehicles 23

Pseudonym generation - Step 1 24 RA RSU -> * {RSU ID, Cert DMV (RSU pub ||RA pub ), RSU loc } RSU-ID A RSU-ID B

Pseudonym generation - Step 2 25 V -> RSU: {ID, RSU ID, T V, (k + t)} RA pub RA

Pseudonym generation - Step 3 26 RA -> RSU: {H(ID,N i ), V pub, (k+t), T v } RA CRL List

Pseudonym generation - Step 4 27 RSU –> V: {SK v 1, SK v 2 … SK v k+I,Cert (PK v 1 ||H(ID, N i )), Cert (PK v 2 || H(ID, N i ))...Cert (PK v k+i - H(ID, N i ))} V pub, T v RA

Revocation Protocol  Malicious vehicles need to be isolated from the network  Revocation of vehicles should be done progressively.  Neighboring vehicles report the violation and the pseudonym used to the next RA via the nearest RSU  RA determines the severity of the violation and forwards the pseudonym to the Central Authority 28

Contd..  CA obtains the mapping of the pseudonym and the vehicle’s identity  Puts the vehicle in the Revocation List  Distributes a copy of the Revocation list to all the RA’s  Takes appropriate action on the malicious vehicle 29

Broadcast Authentication in VANETs  Outline:  Introduction to VANET Technology  Security requirements in VANET technology  Privacy protection in VANET  The proposed Protocol  Fast Authentication in VANET  Security Analysis  Implementation and Future Work  References 30

Enhanced Fast Authentication  First proposed in “Flooding-Resilient Broadcast Authentication for VANETs”  Secures single-hop periodic messages.  Replaces expensive digital signature technique with efficient hash operations. 31

Step 1: Location prediction  Predict location information ( ) over the next “I” beacons  Construct a prediction table for each beacon. 32

Step 2: One Time Signatures  Makes use of Huffman coding for generating OTS.  Construct Huffman binary tree for each beacon.  Chain the “ I ” Huffman trees for the “ I ” beacons to form a Chained Huffman tree (CHT).  The root of the CHT is the one time signature for the authentication of the “ I ” beacons. 33

Step 2: One Time Signatures 34

Step 3: Signature Broadcast  Commitment of the tree Pkots must be authenticated to all receivers via the generated pseudonyms.  Send first beacon B 0 = {m 0,S(m 0 ), cert} where, m 0 = {T 0,L 0,PKots,Dx,Dy}  After commitment is authenticated, send “m i ” and off- path values of the CHT as the signature. 35

Enhanced Pseudonym usage  Construct a Huffman tree for “I” beacons and include the commitment in first beacon B 0  Vehicles cannot authenticate messages if B 0 is not received.  Send PK ots every “ k ” beacons. (k < I).  Include “ k ” when requesting for pseudonyms.  In addition always maintain “t” minimum pseudonyms in OBU.  “ t “ can be varied according to the network conditions. 36

Foreseen Advantages  Parallelize the process of pseudonym generation and beacon prediction. The vehicle can make the request for the pseudonyms and perform the beacon prediction and PK ots generation.  Lesser signature operations.  Not vulnerable to RSU attacks. 37

Broadcast Authentication in VANETs  Outline:  Introduction to VANET Technology  Security requirements in VANET technology  Privacy protection in VANET  The proposed Protocol  Fast Authentication in VANET  Security Analysis  Implementation and Future Work  References 38

Security Analysis  The protocol is secure against DoS attacks: Each vehicle spends a ltd. amount of time in RSU range. Vehicle accepts only the pre-calculated no. of pseudonyms it requested for. RA and RSU have very high computation power. 39

 The protocol is secure against replay attacks: Vehicles and the nodes are tightly synchronized. Include T v in the message  The protocol is secure against vehicular impersonation attacks: Ensure that the vehicle ID is never revealed in the open. TPD ensures that the keys are not revealed to user. 40

 The protocol is secure against RSU impersonation: RA can determine RSU compromise based on the complaints received. An RSU compromise affects communication only in the range of the particular RSU 41

Broadcast Authentication in VANETs  Outline:  Introduction to VANET Technology  Security requirements in VANET technology  Privacy protection in VANET  The proposed Protocol  Fast Authentication in VANET  Security Analysis  Implementation and Future Work  References 42

Simulations in VANET  VANET simulations require both networking component and mobility component.  Usually represented by two different simulators.  Mobility simulator generates the mobility of vehicles  Network simulator provides feedback and modifies trace files accordingly. 43

Our Simulation: Mobility simulation  Simulation of Urban Mobility (SUMO)  Have developed XML scripts to define the topology and the vehicular movement in SUMO. 44

Our Simulation: Network simulation  Use Omnet ++ for network simulation  Veins simulation environment interface between the network simulation and mobility.  INET framework to simulate wireless transmissions 45

Future Work  Continue working on network simulation part for performance evaluation.  Optimize the protocol and enhance the bandwidth efficiency and robustness of this scheme 46

References [1] Hsiao, H.-C., Studer, A., Chen, C., Perrig, A., Bai, F., Bellur, B., Iyer, A.:"Flooding- Resilient Broadcast Authentication for VANETs". [2] Z. Li, Z. Wang, and C. Chigan, “Security of Vehicular Ad Hoc Networks in Intelligent Transportation Systems,” [3] – Nice videoshttp:// [3] 47

Thank You 48