Chris Karlof and David Wagner Secure Routing in Wireless Sensor Networks: Attacks and Countermeasures Chris Karlof and David Wagner

Key Contributions Secure routing issues in WSNs Show how they are different from ad hoc networks Introduce two new classes of attacks Sinkhole attack Hello flood attack Analyze security aspects of major routing protocols Discuss countermeasures & design considerations for secure routing in WSNs

WSNs vs. Ad Hoc Networks Multi-hop wireless communications Ad hoc nets: communication between two arbitrary nodes WSNs Specialized communication patterns Many-to-one One-to-many Local communication More resource constrained More trust needed for in-network processing, aggregation, duplicate elimination

Assumptions Insecure radio links Malicious nodes can collude to attack the WSN Sensor are not tamper-resistant Adversary can access all key material, data & code Base station is trustworthy Aggregation points may not be trustworthy

Threat Models Device capability Attacker type Mote class attacker Laptop class attacker: more energy, more powerful CPU, sensitive antenna, more radio power Attacker type Outside attacker: External to the network Inside attacker: Authorized node in the WSN is compromised or malicious

Security Goals Secure routing Support integrity, authenticity, availability of messages in presence of attack Data confidentiality

Potential Attacks Attacks on general WSN routing Attacks on specific WSN protocols

Attacks on General WSN Routing Protocols Spoof, alter, or replay routing info. Create loops, attack or repel network traffic, partition the network, attract or repel network traffic, etc. Selective forwarding Malicious node selectively drops incoming packets

Sinkhole attacks Specific to WSNs All packets are directed to base station A malicious node advertises a high quality link to the base station to attract a lot of packets Enable other attacks, e.g., selective forwarding or wormhole attack

Sybil attack Wormholes A single node presents multiple ID’s to other nodes Affect geographic routing, distributed storage, multi-path routing, topology maintenance Wormholes Two colluding nodes A node at one end of the wormhole advertises high quality link to the base station Another node at the other end receives the attracted packets

Hello flood attack Acknowledge spoofing Specific to WSNs In some protocols, nodes have to periodically broadcast “hello” to advertise themselves Not authenticated! Laptop-class attacker can convince it’s a neighbor of distant nodes by sending high power hello messages Acknowledge spoofing Adversary spoofs ACKs to convince the sender a weak/dead link support good link quality

Attacks on Specific Routing Protocols TinyOS beaconing Construct a BFS rooted at the base station Beacons are not authenticated! Adversary can take over the whole WSN by broadcasting beacons

Directed diffusion Geographic routing Replay interest Selective forwarding & data tampering Geographic routing Adversary false, possibly multiple, location info. Create routing loop GEAR considers energy in addition to location Laptop-class attacker can exploit it

Countermeasures Shared key & link layer encryption Prevent outsider attacks, e.g., Sybil attacks, selective forwarding, ACK spoofing Cannot handle insider attacks Wormhole, Hello flood, TinyOS beaconing Sybil attack Every node shares a unique secret key with the base station Create pairwise shared key for msg authentication Limit the number of neighbors for a node Hello flood attack Verify link bidirectionality Doesn’t work if adversary has very sensitive radio

Wormhole, sinkhole attack Cryptography may not help directly Good routing protocol design Geographic routing Location verification Use fixed topology, e.g., grid structure Selective forwarding Multi-path routing Route messages over disjoint or Braided paths Dynamically pick next hop from a set of candidates Measure the trustworthiness of neighbors

Authenticated broadcast Base station floods blacklist uTESLA Base station floods blacklist Should be authenticated Adversaries must not be able to spoof

Conclusions WSN security is challenging, new area of research This paper covers security issues at network layer