Secure Neighbor Discovery in Wireless Networks Marcin Poturalski, Panos Papadimitratos, Jean-Pierre Hubaux 1

Neighbor Discovery (ND) “Who are my neighbors?” In wireless networks: “Can I communicate directly with B?” Fundamental Building Block 2

Neighbor Discovery: Routing in ad-hoc networks C A 3 B

Naïve Neighbor Discovery A B “A: Hello” 4 A is a neighbor

Naïve ND: relay attack C B A “A: Hello” 5 A is a neighbor “A: Hello” PHY preamble… MAC A …… IP A …“A:Hello”…… PHY preamble… MAC A …… IP A …“A:Hello”……

Routing in ad-hoc networks: Violation of ND 6 B A C D M

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ND is an important and fragile building block Secure ND protocols have been proposed – Distance Bounding Does not quite solve the problem… To what extent is secure ND possible? 8

Outline Model of wireless networks – language: set theory, 1 st order logic Specification of ND Investigate two classes of protocols: – Time-based (T-protocols) – Time- and Location-based (TL-protocols) Results: – T-protocol ND impossibility (general case) – T-protocol solving ND (restricted case) – TL-protocol solving ND (general case) 9

Model 10

Traces and events Trace is a set of events 11 A B C

SS  S,P Feasible traces System execution: feasible trace Traces feasible with respect to: - setting S - protocol P - adversary A 12  S,P,A 

Setting 13 { A, B, C, D, E, F, G, H } ……… H A C B D G F E

Trace  feasible wrt setting S Causal and timely message exchange A B 14 v – signal propagation speed

Trace  feasible wrt setting S Causal and timely message exchange 15

Local trace 16 A B

17 Local view

Protocol 18 Actions:

19 Correct nodes follow the protocol Trace  feasible wrt protocol

Trace  feasible wrt adversary 20 Adversarial nodes can only relay messages, with minimum delay A

21 Neighbor Discovery Specification

Neighbor Discovery specification 1)Discovered neighbors are actual neighbors 2)It is possible to discover neighbors 22 Protocol P solves Neighbor Discovery for adversary A if

Neighbor Discovery specification 1)Discovered neighbors are actual neighbors 2)It is possible to discover neighbors 23 Protocol P solves Neighbor Discovery for adversary A if in the ND range R … 2-party ND

Results T-protocol ND impossibility (general case) T-protocol solving ND (restricted case) TL-protocol solving ND (general case) 24

Results T-protocol ND impossibility (general case) T-protocol solving ND (restricted case) TL-protocol solving ND (general case) 25

T-protocol impossibility 26 No T-protocol can solve Neighbor Discovery for adversary if Proof (sketch): Any T-protocol P which satisfies ND 2 cannot satisfy ND 1

T-protocol impossibility 27 A B C A B

T-protocol impossibility 28 A B

T-protocol impossibility 29 A B A B C

T-protocol impossibility Trace  b is feasible in S b A declares B a neighbor in  b A and B are not neighbors in S b ND 1 is violated 30 A B C C A B

Results T-protocol ND impossibility (general case) T-protocol solving ND (restricted case) TL-protocol solving ND (general case) 31

Temporal packet leash: T-protocol solving ND 32

Results T-protocol ND impossibility (general case) T-protocol solving ND (restricted case) TL-protocol solving ND (general case) 33

TL-protocol solving ND “Geo-Temporal” packet leash: 34

Conclusion Investigation of Neighbor Discovery in wireless networks for two general classes of protocols T-protocols can solve ND iff TL-protocols can solve ND if 35

Conclusion Problems with proposed protocols: – require synchronized clocks – require very accurate time measurements – require line-of-sight communication (TL) – require secure location (TL) 36

Future work Reasoning about a wider range of protocols – e.g. Challenge-Response schemes Multi-party ND? Moving closer to the physical layer – ? 37