Intrusion Tolerance for NEST

1. Intrusion Tolerance for NEST Bruno Dutertre, Steven Cheung SRI International

2. Outline • Objectives • Proposed approach: • Local authentication and initial key establishment • Leveraging local trust • Intrusion detection and response • Plan

3. Objective • Low-cost key management for large-scale networks of small wireless devices • Constraints: • Limited memory, processing power, and bandwidth • Networks too large and not accessible for manual administration/configuration • Devices can be compromised

4. Traditional Key Management • Decentralized approaches: • Public-key infrastructure • Diffie-Hellman-style key establishment • Approaches based on symmetric-key cryptography • Trusted authenticationand key distribution server (e.g., Kerberos) Too expensive Limited scalability High administrativeoverhead to set up long-term keys Vulnerable to serverfailure Server may be a bottleneck

5. Proposed Approach • Goals: • Intrusion-tolerant architecture for key management in NEST • Use only inexpensive cryptographic algorithm (symmetric-key crypto) • Decentralized (no server) and self organizing • Approach: • Build initial secure local links • For nonlocal communication, rely on chains of intermediaries • Use secret sharing when intermediaries are not fully trusted • Develop complementary intrusion detection methods to locate nontrustworthy nodes

6. Bootstrapping • Establish secure local links between neighbor devices quickly after deployment • Weak authentication is enough (need only to recognize that your neighbor was deployed at the same time as you) • Exploit initial trust (it takes time for an adversary to capture/compromise devices) • Focusing on local links improves efficiency

7. Basic Bootstrapping Scheme • For a set S of devices to be deployed • Construct a symmetric key K • Distribute it to all devices in the set • K enables two neighbor devices A and B • To recognize that they both belong to S (weak authentication) • To generate and exchange a key for future communication • Possible drawback: • Every device from S in communication range of A and B can discover . More robust variants are possible.

8. Leveraging Local Trust B C • To establish keys between distant nodes: • use chains of trusted intermediaries • To tolerate compromised nodes: • disjoint chains and secret sharing D A E

9. Tradeoffs • Security increases with • the number of disjoint paths • the number of shares but these also increase cost • Challenges: • Implement cheap crypto and secret sharing techniques • Quantify the security achieved • Find the right tradeoff for an assumed fraction of compromised nodes

10. Intrusion Detection • Goals: • Detect compromised nodes (to remove them from chains) • Detect other intrusions: denial-of-service attacks, attempt to drain power • Cryptography is ineffective against these

11. Intrusion Detection Approach • Develop models of attacks and relevant signature: • What must be monitored? • How to collect and distribute the data? • Develop diagnosis methods: • Identify the source of the attack if possible • Possible responses: • Avoid nodes that are considered compromised • Hibernation to counter DoS or power-draining attacks

12. Experimental Evaluation • Platform: • “motes” with TinyOS • up to 20% compromised nodes • Objective: show feasibility, measure overhead • Experiment scenario remains to be defined

13. Schedule