Physical Layer Attacks on Unlinkability in Wireless LANs

Recent work has focused on hiding explicit network identifiers such as hardware addresses from the link layer to enable anonymous communications in wireless LANs. These protocols encrypt entire wireless packets, thereby providing unlinkability. However, we find that these protocols neglect to hide identifying information that is preserved within the wireless physical layer. We propose a technique using commodity wireless hardware whereby packets can be linked to their respective transmitters using signal strength information, thus degrading users’ anonymity. We discuss possible countermeasures, but ultimately we argue that controlling information leakage at the physical layer is inherently difficult.