1. Computer Science Using Directional Antennas to Prevent Wormhole Attacks Stephen Thomas Acknowledgement: Portions of this presentation have been donated by Dr. David Evans

2. Computer Science Situation: Ad Hoc Beacon Routing 0 1 2 3 4 Nodes select parents based on minimum hops to base station

3. Computer Science Wormhole Attack S D A B C Attacker needs a transceivers at two locations in the network, connected by a low latency link Attacker replays (selectively) packets heard at one location at the other location X Y

4. Computer Science Wormhole Attack on Beacon Routing 0 1 2 X Y 0 1 2 Wormhole attack disrupts network without needing to break any cryptography!

5. Computer Science Possible Solutions Packet Leashes [Hu, Perrig, Johnson 2003] –Requires tightly synchronized clocks (temporal leashes) or precise location information (geographic leashes) –Signal is transmitted at speed of light –Calculate if packet could travel distance between nodes in packet lifetime Packet Arrival Direction

6. Computer Science Directional Antennas General benefits: power saving, less collisions 1 23 4 56 North Aligned to magnetic North, so zone 1 always faces East Omnidirectional Transmission Directional Transmission from Zone 4

7. Computer Science Assumptions Legitimate nodes can establish secure node-node links –All critical messages are encrypted Network is fairly dense Nodes are stationary Most links are bidirectional (unidirectional links cannot be established) Transmissions are perfect wedges Nodes are aligned perfectly (relaxed in paper)

8. Computer Science Directional Neighbor Discovery A 1. A  RegionHELLO | ID A Sent by all antenna elements (sweeping) 2. B  AID B | E KBA (ID A | R | zone (B, A)) Sent by zone (B, A) element, R is nonce 3.A  BR Checks zone is opposite, sent by zone (A, B) B zone (B, A) = 4 is the antenna zone in which B hears A 1 23 4 56

9. Computer Science A B zone (B, A[Y]) = 4 zone (A, B [X]) = 1 Undetected False Neighbor: zone (A, B) = opposite of zone (B, A) Not Detecting False Neighbors 1 23 4 56 X Y Directional neighbor discovery prevents 1/6 of false direct links…but doesn’t prevent disruption

10. Computer Science V Verified Neighbor Discovery 1. A  RegionAnnouncement, done through sequential sweeping 2. B  AInclude nonce and zone information in the message 3. A  BCheck zone information and send back the nonce A B 4. INQUIRY | ID B | ID A | zone (B, A) 5. ID V | E KBV (ID A | zone (V, B)) Same as before 4. B  RegionRequest for verifier to validate A 5. V  BIf V is a valid verifier, sends confirmation 6. B  AAccept A as its neighbor and notify A

11. Computer Science Verifier Analysis v B A Region 1 Region 2 X Y 1 23 4 56 1 23 4 56 Wormhole cannot trick a valid verifier: zone (V, A [Y]) = 5 zone (A, V [X]) = 1 Not opposites: verification fails

12. Computer Science Worawannotai Attack v B A Region 1 Region 2 X 1 23 56 23 4 56 V hears A and B directly A and B hear V directly But, A and B hear each other only through repeated X

13. Computer Science Preventing Attack 1. zone (B, A)  zone (B, V) 2. zone (B, A)  zone (V, A) 3. zone (B, V) cannot be both adjacent to zone (B, A) and adjacent to zone (V, A)

14. Computer Science Connectivity and Routing 0 1 2 3 4 5 6 7 8 9 10 4 6 8 12 14 16 18 20 Average Path Length Omnidirectional Node Density Strict Protocol Trust All Verified Protocol Network with density = 10 Verified protocol: 0.5% links are lost no nodes disconnected Strict protocol: 40% links are lost 0.03% nodes disconnected 20% path increase from verified

15. Computer Science Vulnerabilities Attacker with multiple wormhole endpoints –Can create packets coming from different directions to appear neighborly Magnet Attacks –Protocol depends on compass alignment of nodes Antenna, orientation inaccuracies –Real transmissions are not perfect wedges

16. Computer Science Conclusion An attacker with few resources and no crypto keys can substantially disrupt a network with a wormhole attack If you know your neighbors, can detect wormhole Need to cooperate with your neighbors to know who your legitimate neighbors are

17. Computer Science Future Work Analysis of protocol vulnerabilities to other attacks –Magnet for disruption (not pertaining to wormhole attacks) –Flipping nodes to disorient north from south Expand protocol to handle dynamic ad hoc networks

18. Computer Science Thank you! Questions?