SeCoWiNet 2007

FAMIC

Fast Authentication and Message Integrity Check in Vehicular Communications

Nikodin Ristanovic Papadimitratos Panos George Theodorakopoulos Jean-Pierre Hubaux

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Intro

•IVC – Inter-Vehicle Communication expected to play a significant role in VNs

•Multi-hop communication difficult to avoid (both 802.11 and IEEE 1609 suite of WAVE standards designed for short range communication)

•OUR FOCUS: end-to-end delay of messages; more precisely the component of the delay caused by message processing in intermediate nodes

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Quick reminder

•An existing architecture that we build upon

•Provides authenticated and integer communication

•Tries to protect privacy

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Security costs

• eCrypt project • ppc 32 533MHz, Motorola powerPC G4 7410

• Microsoft Windows Mobile for Automotive 1.0

• Expected frequency of safety messages (every 300ms)• Many of these messages not interesting for receiving node

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Motivating example

• Congestion notification application [17],[18]• Vehicles expected to relay messages for each

other – Observation 1)• Limited scope of the adversaries – Observation 2)

•An adversary = a non-legitimate node sending forged messages

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Our Idea

•Reverse the order of operations!

Type of Message

Time ...DestinationSource Data

Sender’s Signature Sender’s Public Key CA’s Certificate of PK

1

2

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The scheme - FAMIC

Quick Filter – Am I interested

in this message ?

Check integrity of the message,

authenticate

OK Use and/orForward

…Queue

reduce/increase

check rate

Background check Forward

Alert/OK

Alert/OK

ToMTime …Source loc.Dest. loc. Sender’s sign.Sender’s PKCA’s cert. of PK

Yes

No

“Relaxed” vs. “Check all” mode

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Security issues

•Performance improved, but certain security risks introduced

•Some messages are relayed without prior authentication and integrity check

•DoS attack– The goal: increase the amount of forged

traffic in the network (i. e. degrade the whole service)

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The game in strategic form

2p

2p

- decides if the message receives is going to be forged or not - decides whether to check the received message or not

1p

463 0 ccc

5121 0 cccc (1)

(2)

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Best response functions

•For a finite strategy space (i.e. for so called finite games), the payoff of each player to profile is given by:

ii Ss

iiiiii susu ,

i

• - the profile;

• - the pure strategies of the players

ii Ss

(3)

6341 11 ycxcyxcxyu

15122 11 cyxyxcccxyu

(4)

(5)

xy

- probability that a received message is forged

- probability of checking the message that is going to be relayed

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The result

52

1

cc

cxe

643

3

ccc

cye

),( ee yx

(6) (7)

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Interpretation

153 cc

9.0214 ccc12 c

05.0ex5.0ey

1.016 cc (8)

(9)

(11)

(10)

Mixed strategy equilibrium:

Example:

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Performance evaluation

•We consider the scheme with only two modes of operation:– “relaxed” mode of operation– “check all” mode of operation

•Performance improved over 40% under very realistic assumptions

•Up to 80% under some stronger assumptions

•Very good responsiveness even when the adversary tries to “keep a low profile”

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Example

• 10% of the network under attack, on average

• 10% checking rate in “relaxed” mode of operation (this concerns the messages that are only relayed)

19.0

1.09.0

1*1.01.0*9.0

tt

ttRrelayed

Legitimate node

10% of the time in “relaxed” mode of operation

90% of the time in “check all” mode of operation

(12)

relayedR - the average checking rate of the messages that are only supposed to be relayed

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Reduced security costs

0 10 20 40 60 80 100

0 0.19

0.28 0.46 0.64 0.82 1

relayedR

%attackI

relayedR

%attackI

- the average checking rate of the messages that are only supposed to be relayed

- the percentage of the network under attack (on average)

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Performance boost

•Previous assumptions +50% of the received messages have the receiving node as destination; the other 50% are relayed;

20% of the received messages have the receiving node as destination; the other 80% are relayed;

relayedR

%attackI

- the average checking rate of the messages that are only supposed to be relayed

- the percentage of the network under attack (on average)

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Responsiveness•1Mbps – incoming traffic per node

•1.5kB – message size

• 83 messages/s

•10% nodes are adversaries

• 0.9 – the probability that a received message is valid

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sttrigg 64.283

220

(13)

(14)

triggt - time needed to detect the threat and switch from “relaxed” to “check all” mode of operation

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Triggering times

triggtmsgF

- time needed to detect the threat and switch from “relaxed” to “check all” mode of operation

triggt

- the percentage of fake messages in the network

•Quick reaction to the presence of an adversary means that the injected forged messages are kept locally

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Discussion and related work

•The same approach can be applied to messages that ARE destined for the node

•Advanced classification of messages – ephemeral trust

•M. Raya, P. Papadimitratos, J.-P. Hubaux– ECDSA, NTRU – key size vs. delay– Correlation – ignoring the redundant messages

(safety message broadcast frequency – typically, every 300ms)

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Conclusion

•Reactive vs. proactive approach

•We question the necessity of strong security measures under certain assumptions

•We show that for a group of applications that adhere to certain observations, the increase in performance can be significant

•We believe it is worth further investigation

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References (1)• M. Raya, P. Papadimitratos, and J.-P. Hubaux, Securing Vehicular

Communications, In IEEE Wireless Communications Magazine, Special Issue on Inter-Vehicular Communications, October 2006.

• F. Dotzer, T. Kosch, M. Strassberger, Classification for traffic related inter-vehicle messaging, 5th IEEE International Conference on ITS Telecommunications, Brest, France, June 27-29, 2005.

• Naoki Shibata, Takashi Terauchi, Tomoya Kitani, Keiichi Yasumoto, Minoru Ito, Teruo Higashino. A Method for Sharing Traffic Jam Information using Inter-Vehicle Communication. Mobile and Ubiquitous Systems: Networking & Services, 2006 Third Annual International Conference

• http://www.ecrypt.eu.org/ebats/

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References (2)

• M. Mauve, A. Widmer, H. Hartenstein, A Survey on Position-Based Routing in Mobile Ad-Hoc Networks in Network, IEEE, Nov/Dec 2001

• Windows Mobile for Automotive 1.0: http://www.microsoft.com/windowsautomotive/wma/default.mspx

• "Security and Cooperation in Wireless Networks" by Levente Buttyan and Jean-Pierre Hubaux

• Alaeddine El Fawal, Jean-Yves Le Boudec, Kave Salamatian.Self-Limiting Epidemic Forwarding. LCA-REPORT-2006-126, 2006

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Questions?Answers

?Q&A