Intrusion Tolerance for NEST Bruno Dutertre, Steven Cheung SRI International

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

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

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

Proposed Approach Goals: Approach: 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

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

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.

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

Tradeoffs Security increases with but these also increase cost 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

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

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

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

Schedule