  The intrinsic hardware imperfection of WiFi chipsets manifests itself in the
transmitted signal, leading to a unique radiometric fingerprint. This
fingerprint can be used as an additional means of authentication to enhance
security. In fact, recent works propose practical fingerprinting solutions that
can be readily implemented in commercial-off-the-shelf devices. In this paper,
we prove analytically and experimentally that these solutions are highly
vulnerable to impersonation attacks. We also demonstrate that such a unique
device-based signature can be abused to violate privacy by tracking the user
device, and, as of today, users do not have any means to prevent such privacy
attacks other than turning off the device.
  We propose RF-Veil, a radiometric fingerprinting solution that not only is
robust against impersonation attacks but also protects user privacy by
obfuscating the radiometric fingerprint of the transmitter for non-legitimate
receivers. Specifically, we introduce a randomized pattern of phase errors to
the transmitted signal such that only the intended receiver can extract the
original fingerprint of the transmitter. In a series of experiments and
analyses, we expose the vulnerability of adopting naive randomization to
statistical attacks and introduce countermeasures. Finally, we show the
efficacy of RF-Veil experimentally in protecting user privacy and enhancing
security. More importantly, our proposed solution allows communicating with
other devices, which do not employ RF-Veil.
