1. 1 Covert Communication based Privacy Preservation in Mobile Vehicular Networks Rasheed Hussain*, Donghyun Kim**, Alade O. Tokuta**, Hayk M. Melikyan**, and Heekuck Oh*** *Department of Computer Science, Innopolis University, Kazan, Russia ** Department of Mathematics and Physics, North Carolina Central University, Durham, NC, USA ***Department of Computer Science and Engineering, Hanyang University, South Korea

2. 22 Agenda Introduction Problem Statement Covert Communication-based Privacy Preservation – Protocol Outline –Covert Communication –Proposed Covert-based Scheme Quantitative Evaluation Conclusions and Future Work

3. 33 Introduction Vehicular Ad hoc NETwork (VANET) –Vehicle-to vehicle (V2V) and vehicle-to-infrastructure (V2I) communication paradigms –Driving safety-related and the other applications –IEEE 802.11p standard mandates broadcasting beacon messages in the order of milliseconds

4. 44 Agenda Introduction Problem Statement Covert Communication-based Privacy Preservation – Protocol Outline –Covert Communication –Proposed Covert-based Scheme Quantitative Evaluation Conclusions and Future Work

5. 5 Problem Statement Privacy is of prime concern in VANET Current solutions include: –Mix Zones, silent periods –Identityless schemes –Multiple pseudonyms (mostly used) However, even multiple pseudonyms do not necessarily preserve the privacy –Statistically, possible to link multiple pseudonyms to one entity [1] [1]. Wiedersheim et al. “Privacy in inter-vehicular networks. Why simple pseudonym change is not enough,” IEEE WONS, pp. 176–183, 2010.

6. 66 Problem Statement – cont’ How to prevent the statistical attack? –Assign multiple pseudonyms to nodes –Let nodes exchange their pseudonyms with each other Pseudonyms exchange should be carried out on a covert channel established on top of existing beaconing framework –Exchange their pseudonyms in corrupt beacons with the help of a shared secret (key) among the exchanging parties Revocation should be still possible [8] provides an outline, but is without a firm detail

7. 77 Agenda Introduction Problem Statement Covert Communication-based Privacy Preservation – Protocol Outline –Covert Communication –Proposed Covert-based Scheme Quantitative Evaluation Conclusions and Future Work

8. 8 Protocol Outline Design Rationale –Identity exchange-based privacy preservation Unintended should not determine whether the exchange happens Intermingle the exchange messages part of normal conversation –Conditionally deniable –Privacy-preserving Minimize the use of cryptography and use natural ways to secure the communication No need for additional infrastructure or message structure to add this functionality Using others’ pseudonyms is good until and unless you can trace back when needed

9. 9 Protocol Outline – cont’ Design Goals –Exchange pseudonyms for privacy preservation –Use covert channel to exchange the pseudonyms Only intended receivers know the position of the information in the corrupted beacon –Provision of anonymity through pseudonym exchange –Unlinkability through pseudonym-exchange ? ? ?

10. 10 Covert Communication Observation: Wireless is Noisy –Noise is a non-stationary and random process –Idea: Use the random properties of wireless channel noise to hide secret message Packet corruption can be caused by interference, multipath, non-wifi, collisions, hidden terminals, low signal strength, etc. Hide messages in corrupted packets Challenge: Make message indistinguishable from “normal” corruption

11. 11 Covert Communication – cont’ Rivest et al. “Chaffing and Winnowing: Confidentiality without Encryption.” Cryptobytes 4:1 pp. 12–17. 1998 Chaffing and Winnowing [9] –Chaff the actual corrupted frames on the channel due to packet corruption –Grain the crafted frames which are deliberately corrupted by the sender for the secret communication Two main security measures –Geolock key: spatio-temporal group secret –Session key: help to locate pseudonym from a corrupted-looking beacon

12. 12 Proposed Covert-based Scheme Security Goals –Deniable Ability to deny the communication –Anonymous Cannot be identified specifically –Confidential Adversary cannot recover message –Robustness Cannot be disrupted

13. 13 Proposed Covert-based Scheme Threat Model –Passive adversary Figure out the possible hidden communication Wireless comm. is prone to such experiences –From the messages, adversary wants to figure out who exchange identity with whom This leads to the traditional privacy and profilation problems –Adversary is semi-global for some physical area Accumulates the messages in that area to figure out the identity exchange messages –Ephemeral networks are going to be a challenge for even sophisticated adversary

14. 14 Proposed Covert-based Scheme [1/11] Network Model

15. 15 Proposed Covert-based Scheme [2/11]

16. 16 Proposed Covert-based Scheme [3/11]

17. 17 Proposed Covert-based Scheme [4/11] Pseudonym table at DMV Pseudonym table at RA

18. 18 Proposed Covert-based Scheme [5/11]

19. 19 Proposed Covert-based Scheme [6/11] Can be intentionally corrupted Sender’s pseudonym Actual pseudonym to be exchanged Length of pseudonym Shared key Replace CRC

20. 20 Proposed Covert-based Scheme [7/11]

21. 21 Proposed Covert-based Scheme [8/11] Hussain et al. “Secure and privacy-aware traffic information as a service in VANET-based clouds” in press, Pervasive and Mobile Computing, Elsevier, 2015 Only small number of spatio-temporal users can make this

22. 22 Proposed Covert-based Scheme [9/11]

23. 23 Proposed Covert-based Scheme [10/11]

24. 24 Proposed Covert-based Scheme [11/11] Revocation algorithm

25. 25 Agenda Introduction Problem Statement Covert Communication-based Privacy Preservation – Protocol Outline –Covert Communication –Proposed Covert-based Scheme Quantitative Evaluation Conclusions and Future Work

26. 26 Quantitative Evaluation [1/4]

27. 27 Quantitative Evaluation [2/4]

28. 28 Quantitative Evaluation [3/4] Computation and Communication Overhead –Comm. overhead is the modified beacon frequency –Revocation cost Direct revocation Indirect revocation Direct revocation is done when the sender of pseudonym is the owner of pseudonym, whereas indirect revocation is done when the pseudonym is exchanged with someone else

29. 29 Quantitative Evaluation [4/4] Comparison with known schemes

30. 30 Agenda Introduction Problem Statement Covert Communication-based Privacy Preservation – Protocol Outline –Covert Communication –Proposed Covert-based Scheme Quantitative Evaluation Conclusions and Future Work

31. 31 Conclusions and Future Directions Privacy preservation in VANET Identity-exchange based mechanism –Pseudonyms are exchanged on a covert channel –Conditional privacy guarantees revocation Future Work –Implementation of covert communication –Incorporate the protocol to existing work for privacy enhancement –Optimize covert channel in broadcast environment –Pseudonym exchange at multiple levels