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Trustworthy Wireless. Jeffrey Pang, Srinivasan Seshan Ben Greenstein, Ramakrishna Gummadi, Tadayoshi Kohno, David Wetherall. Why You Should Worry About Wireless Privacy. Ubiquity of 802.11 Networks. (typically < 100m). Cheap Radios, Monitoring Software. Ubiquity of 802.11 Devices.

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Trustworthy Wireless

Jeffrey Pang, Srinivasan SeshanBen Greenstein, Ramakrishna Gummadi, Tadayoshi Kohno, David Wetherall

Why You Should Worry About Wireless Privacy

Ubiquity of



(typically < 100m)

Cheap Radios,



Ubiquity of




802.11 Access Points in Chicago

What Your Wireless Traffic Says About You

Can Your Wireless Traffic Identify You?

Can Your Wireless Traffic Reveal Where You’ve Been?

  • Yes: MAC address = unique identifier
  • Previously proposed solution: Pseudonyms (change MAC address each session)
  • Pseudonyms are not enough!
  • Implicit identifiers remain (exposed characteristics of network traffic)
  • Yes: Laptops probe for network names you’ve connected to before
  • Network names (SSIDs) are often identifying (e.g., “CMU,” “IR Guest,” “Bob Home”)
  • Fundamental Problem: device discovery and pairing is not private

Implicit Identifier Examples

Example of Where You’ve Been

Network destinations: web bookmarks, your email server, VPN server, etc.

Wireless Network Names: networks you’ve visited before (e.g., your home)

802.11 Protocol Fields: wireless card implementation and configuration

Packet Sizes: size of broadcast packets (NetBIOS, MS Office, mDNS, etc.)

(1) Collect some wireless data…

“Anonymized” SIGCOMM 2004 802.11 Trace

Visible even with

WPA,WEP encryption!

“djw” = David J. Wetherall’s Home Network?

(2) Lookup suspect SSID in a war driving database…

Implicit Identifier Accuracy

Example: 1 in 4 users identified >50% of the time with 0.1% false positives

(3) Find suspect’s home using Google Maps!




Typical Hotspot

Best Practices