Security in Wireless Sensor Networks

1. Security in Wireless Sensor Networks Perrig, Stankovic, Wagner Jason Buckingham CSCI 7143: Secure Sensor Networks August 31, 2004

2. Introduction to sensor networks • Security Issues • Key establishment & setup • Secrecy & Authentication • Privacy • Robustness to DOS • Secure Routing • Resilience to node capture • Secure Group Management • Intrusion Detection • Secure Data Aggregation • Secure Sensor Network Research

3. Broad Range of Applications • Wildlife Monitoring • Machinery Performance • Building Safety • Military Applications • Health Monitoring • Countless other applications Most applications require some level of security!

4. Traditional security cannot be applied directly • Sensor device limitations • Power, Processing, and Communication • Nodes are often physically accessible, allowing possible physical attacks • Sensor networks interact with their environments and with people

5. Security Research Issues • These new problems present an opportunity to properly address network security • Security is NOT a standalone component – it must be integrated into every component

6. Key Establishment & Setup • Why not use existing protocols? • Public key cryptography has too much system overhead for sensor networks • Key establishment techniques must scale well to hundreds or thousands of nodes • Sensor nodes have different communication needs

7. Key Establishment - Potential Solutions • Establish a network wide shared key • Problem: if one node is compromised, the whole network is compromised • Instead use shared symmetric keys between each pair of nodes that are preconfigured • Problem: It doesn’t scale well! • For an n node network, each node must store n-1 keys, and n * (n – 1) / 2 total keys are needed. • Combine the above: use a network wide key to establish link keys, then erase the networkwide key. • Problem: New nodes cannot be added after initial deployment

8. Key Establishment - Potential Solutions (cont.) • Bootstrapping Keys • each node shares a single key with the base station and the base station sets up keys between pairs. • Problem: requires a trusted base station that is the central point of failure • Random Key Predistribution – • choose a large pool of symmetric keys, and give each node a random subset of the pool • not all nodes share a common key, but the network will still be fully connected if the probability of two nodes sharing a key is sufficiently high • Problem: once compromising a sufficient number of nodes, attackers could reconstruct the entire pool and break the scheme

9. Secrecy & Authentication – Cryptography • End-to-end cryptography • Provides high level of security, but requires that keys be set up among all end points • Incompatible with passive participation and local broadcast • Link-layer cryptography • Simplifies key setup • Supports passive participation and local broadcast • Problem? Intermediate nodes can eavesdrop and alter messages. Is this really a problem?

10. Cryptography Issues • Performance Costs • Extra computation • Could be reduced by additional hardware but this increases node cost and will it really fix the problem? • Increases packet size • Recent research shows that most of the performance overhead is attributable to increased packet size, not additional computation • This limits how much dedicated cryptographic hardware will help

11. Robustness to Denial of Service • Adversaries can simply broadcast a high-energy signal or violate the 802.11 MAC protocol to disrupt communication • Solutions? • Spread spectrum communication, but cryptographically secure spread spectrum radios are not commercially available • Automated defense, by simply routing around the jammed portion of the network

12. Secure Routing • Current routing protocols suffer security vulnerabilities • DOS attacks, packet injection, replay attacks

13. Resilience to Node Capture • Sensor networks are highly susceptible – the compromise of a single node usually compromises the entire network • This is more of a problem because sensor networks often lack physical security

14. Solutions to Node Capture • Physical solution • tamper resistant packaging • Software: • Create algorithms that use majority voting schemes; send packets along multiple independent paths and check for consistency • Gather redundant data and analyze for consistency

15. Secure Group Management • Groups of nodes perform data aggregation and analysis (tracking a moving object) • The group may change continuously and quickly • Protocols are needed for admitting new group members and supporting secure communication with the group • Solutions conserve time and energy

16. Intrusion Detection • Classic intrusion detection is very expensive in terms of memory, energy, and bandwidth • To develop a solution, typical threat models must be analyzed • Secure groups may be a possible solution for decentralized intrusion detection

17. Secure Data Aggregation • Tons of data can be collected from the various nodes in the network • How do we aggregate the data so as to reduce network traffic to the base station? • Aggregation locations must be secured

18. Privacy • How do we prevent sensor networks from being used to violate privacy? • Devices are becoming smaller, cheaper, and more effective at surveillance • Solutions? • New laws, technological responses, and awareness

19. Other Issues • What cryptographic algorithms are best suited for use in sensor networks? • Public key cryptography? Too expensive! • DES/Triple DES • AES • RC5 • We need something that fits the processing and memory requirements of our nodes

20. Secure Sensor Network Research • How can we build security into sensor networks from the outset? • Advantages of sensor networks • Many applications will be deployed under a single administrative domain • It may be possible to exploit redundancy, scale, and physical characteristics