Implementation and Evaluation of Certificate Revocation List Distribution for Vehicular Ad-hoc Networks Petra Ardelean Advisor: Panos Papadimitratos

Vehicular Ad-hoc Network (VANET) Designed to provide safety and comfort for passengers Using asymmetric cryptography  Certificate Authority (CA) issues certificates  Signature verification using the public key 2

Problem description CRLs are needed for  Excluding compromised, faulty or illegitimate nodes  Preventing the use of compromised cryptographic material How to distribute large CRLs in a reasonable time with low bandwidth utilization? 3

State of the art (1) Papadimitratos et al, Certificate Revocation List Distribution in Vehicular Communication Systems [1]  The CA uses the infrastructure (RSUs) to send the CRLs to the vehicles  Use encoding mechanisms for redundancy 4

State of the art (2) K. Laberteaux et al, Security Certificate Revocation List Distribution for VANET [2]  RSUs used as the first phase of the dissemination  Vehicles broadcast CRL updates to other vehicles 5

State of the art (3) P. Papadimitratos et al, Secure Vehicular Communications: Design and Architecture [3]  Revocation Protocol of the Tamper-Proof Device (RTPD)  Revocation Protocol using Compressed Certificate Revocation (RCCRL)  Distributed Revocation Protocol (DRP) 6

General concept CRL Distribution System RSU3RSU2RSU1 Random encoded pieces 7

CRL Distribution System CA (1) Generate CRL (2) Encode the CRL (3) Sign each piece from (2) Network Communication (1)Compute how many pieces from (3) should be sent to each RSU (2)Send the pieces to the RSUs 8

The Encoding … CRLM parts CRL version Time stamp Sequence number CA ID Encoded CRL piece Signature CA private key Packet format sent to the RSUs … Rabin’s algorithm N pieces, N > M Encoded CRL 9

Packet format sent to the RSUs 1. Verify signature 2. Store CRL piece 3. If enough pieces stored, decode, i.e. reconstruct the CRL CRL version Time stamp Sequence number CA ID Encoded CRL piece Signature CA private key 10 Vehicle – Receiving CRLs

Implementation C++ implementation Using openSSL cryptographic library for  Generating the CRLs  Signing and verifying the encoded pieces Using Rabin’s algorithm as an erasure code 11

Implementation Network Communication Configuration file with the RSUs IP addresses Source routing to send random pieces to each RSU Encoded pieces sent in UDP packets 12

Rabin’s algorithm - Encoding 13 MMMM B NxM A X = N x L W M x L CRL

Rabin’s algorithm - Decoding 14 W’ M x L A’ M x M X = B M x L CRL

Evaluation Settings (1) 15 random encoded pieces CRL Distribution System RSU

Evaluation Settings (2) 16 Laptop configuration CPUIntel 1.8 GHz Operating SystemLinux LibraryOpenSSL 0.9.8g Compilergcc Wireless card802.11b AP configuration Bit rate5.5 Mbps

Evaluation Purposes Examine the system performance by  varying the CRL size  varying the encoding vectors number and length 17

Evaluation Results (1) Figures  show 95% confidence intervals  100 iteration for each experiment M and N variations  M Є [25,100], increasing by 25  N chosen as the redundancy factor is r = N / M is 1.5 Velocity 3 km/h 18

Evaluation Results (2) 19

Evaluation Results (2) 20

Evaluation Results (2) The encoding vectors should be chosen in concordance with the CRL size 21

Evaluation Results (3) 22

Evaluation Results (3) The time to reconstruct the original CRL is inverse proportional with the redundancy factor 23

Conclusion First implementation of a CRL distribution system for VANET Performance measurements conducted on the system 24

Further work Compare the experimental results with simulation results Integrate the CRL Distribution system into the Vehicular Communication project 25

Thank you Questions? 26

Bibliography [1]P. Papadimitratos, G. Mezzour, and J.-P. Hubaux, Certificate Revocation List Distribution in Vehicular Communication Systems, short paper, ACM VANET 2008, San Francisco, CA, USA, September 2008 [2]K. Laberteaux, J. Haas, and Y-C Hu, Security Certicate Revocation List Distribution for VANET, ACM VANET, San Francisco, CA, USA, September 2008 [3]P. Papadimitratos, L. Buttyan, T. Holczer, E. Schoch, J. Freudiger, M. Raya, Z. Ma, F. Kargl, A. Kung, and J.-P. Hubaux, Secure Vehicular Communications: Design and Architecture, IEEE Communications Magazine, November