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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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