Protocol Security for Wireless Networks Yih-Chun Hu Illinois Center for Wireless Systems

Pervasiveness of Security Layers in the Internet divide responsibility Security is important at each layer Physical MAC / Link Network Transport Application a PHY MAC IP TCP, UDP HTTP, IMAP

CIA: Not Just an Intelligence Agency Confidentiality: – Data – Privacy (Location, Identity, Traffic, …) Integrity: – Data Integrity – Origin Integrity (Location, Identity, …) Availability

Solutions Must Pervade Layers Many security properties are vulnerable at several layers: – Availability – Location privacy Physical MAC / Link Network Transport Application

Why Location Privacy? Wireless transmissions can reveal location: – Cellular – Electronic Toll Collection (iPass) – WiFi, Bluetooth, …

Providing Location Privacy Power-control for avoiding localization (Physical) Pseudonymous geographic routing (Network) Anonymous rendezvous (Network) Transaction communication model (Transport) Silent periods (Cross-Layer): – Dissociate one transaction from another – Duration depends on density, mobility User Interface (Application)

Reducing Localization Precision Existing localization techniques: – Rice: less than 1m with 50% error indoors – Place Lab: 15-30m with 50% error outdoors Need (generally) at least 3 APs passively scan all channels order all APs based on their RSSIs: R 1 >= R 2 >= … >= R n exists R 1 -R i-1 <20 dB & R 1 -R i >20 dB? transmit at the maximum power adjust transmit power to TX AP – R i + RS AP -10dB effective area for TPC YES NO

Using Silent Period Decorrelate transmissions: – Deterministic plus random – BusView data validation

User Interface Directs all location privacy mechanisms Privacy on/off checkbox Wait notification

Why Availability? Many different wireless technologies: – Unlicensed bands share spectrum with industrial applications and other users Users running the same protocol might not cooperate: – Selfish misbehavior – Malicious misbehavior – Software and hardware bugs

A Multi-Layer Solution to Availability Jamming mitigation (Physical) Packet leashes (Physical / Network) MAC-level misbehavior detection (MAC) Secure routing protocols (Network)

Possible Misbehavior Do not follow MAC-layer rules for “backoff” Transmit Wait B1 = 1 B2 = 20 Transmit Wait B2 = 19 B1 = 1 Misbehaving node Well-behaved node

Deterministic Backoff Receivers choose the backoff for the senders – Included in the previous acknowledgement DATA Sender S Receiver R CTS ACK(B) RTS B

A Bottom-Up Approach to Availability Start with a trusted core: – (Possibly) a subset of nodes – Very low bandwidth – Highly available Bootstrap services using the core: – Routing – Congestion control Handle failures of core nodes

Wireless Security Faculty at Illinois Tamer Basar Roy Campbell Carl Gunter Christoforos Hadjicostis Yih-Chun Hu Ravishankar K. Iyer Klara Nahrstedt William H. Sanders Nitin H. Vaidya