ITEC 810 – Project Unit Trustworthy Sensor Networks Daniel Aegerter, Supervisor: Rajan Shankaran

Agenda  Problem Statement  Wireless Sensor Networks  Notion of Trust in Wireless Sensor Networks  Comparative Analysis  Recommendations 1

Problem  Security is critical in many applications of Wireless Sensor Networks (WSNs) — Battlefield surveillance — Patient monitoring — Environment monitoring  Security mechanisms assume trustworthiness of participating nodes  What happens if nodes get compromised? — Access key material — Change content of messages — Drop messages  Lives and livelihoods might depend on the correctness of the data 2

Wireless Sensor Networks (WSNs)  Sensor nodes sense data from the environment and detect specific events  Sensor nodes are equipped with sensors to monitor a wide range of physical conditions: — Temperature, Humidity, Light, Pressure, Object motion, Noise, etc.  Sensor nodes are constrained by limited resources 3 Memory Processor Unit Communication device Power Unit Sensor Unit

Network Architecture  Components of Wireless Sensor Networks — Common Sensor Nodes — Base Station  Multihop communication 4

Notion of Trust  “Trust is the subjective probability by which an individual, A, expects that another individual, B, performs a given action on which its welfare depends” (Gambetta, 1988) 5 In the context of WSNs  Trustworthy sensor nodes don’t: — Manipulate gathered information — Alter information received from neighbouring nodes — Flood the network with bogus routing information — Drop messages received from other nodes

Challenges in Evaluating Trust for WSNs  Limited processing, storage, and energy resources — Existing protocols and mechanisms are not applicable — Minimise communication overhead  Trusted authority not present in WSNs — Public key mechanisms and certificates not suitable  Adoption of architectural network changes — Dynamic nature of WSNs — Nodes may become faulty or compromised  Trust re-evaluation is essential 6

Concept of Reputation-Based Trust Systems  Trust is based on a node’s behaviour — Does the node behave in a correct manner? — Network events and correctness of gathered information  Trust evaluation through first and second-hand information — Direct observations — Recommendations from peers  Building blocks — Watchdog mechanism  collects evidence — Reputation system  evaluates and maintains trust 7

Comparative Analysis  Compares five reviewed reputation-based frameworks 1. Reputation-based framework for high integrity sensor network (RFSN) 2. Gaussian trust model and reputation system (GRSSN) 3. Lightweight group based trust management scheme (GTMS) 4. Trust-based cluster head election 5. Certificate and behaviour-based approach  Determines characteristics and constraints of each framework  Proposes categories to conduct the comparative analysis — Trust management — Node and network requirement — Trust evaluation 8

Comparative Analysis – Some Criteria  Evidence — Network events vs. correctness of sensed data  Pre-established trust relationships — Do sensor nodes trust each other at time of deployment?  Storage complexity — Tables, keys, certificates  Revocation — What happens with non-cooperative sensor nodes? 9

Comparative Analysis – Outcomes  All frameworks have some design problems — Difficult to take all characteristics and constraints of WSNs into account  Frameworks are application specific — Different assumptions — Different requirements (e.g. supernodes, keys, certificates)  Sophisticated frameworks are more complex — Economical issues — Management issues  Evidence analysis — Network events or also correctness of sensed data? 10

Recommendations  Collaborative reputation-based approach for establishing trust  Behaviour of nodes is observed by a subset of sensor nodes — Other nodes do not have to monitor network events — Guardian nodes  Guardian nodes evaluate collaborative trustworthiness of nodes — All sensor nodes are directly observable by guardian nodes — Guardian node evaluate whether a node is cooperative — Opinions are shared among guardian nodes  Blacklist entry has to be confirmed by other guardians — Sensor node keep list with non-cooperative nodes 11

Recommendations - Example 12

Future Research Directions  Analyse correctness of sensed data not only network events  Trust evaluation for different roles that sensor node can perform — Forward messages — Aggregate data — Sense information 13 Thank you

Questions 14