  CSI (Channel State Information) of WiFi systems contains the environment
channel response between the transmitter and the receiver, so the
people/objects and their movement in between can be sensed. To get CSI, the
receiver performs channel estimation based on the pre-known training field of
the transmitted WiFi signal. CSI related technology is useful in many cases,
but it also brings concerns on privacy and security. In this paper, we open
sourced a CSI fuzzer to enhance the privacy and security of WiFi CSI
applications. It is built and embedded into the transmitter of openwifi, which
is an open source full-stack WiFi chip design, to prevent unauthorized sensing
without sacrificing the WiFi link performance. The CSI fuzzer imposes an
artificial channel response to the signal before it is transmitted, so the CSI
seen by the receiver will indicate the actual channel response combined with
the artificial response. Only the authorized receiver, that knows the
artificial response, can calculate the actual channel response and perform the
CSI sensing. Another potential application of the CSI fuzzer is covert channels
based on a set of pre-defined artificial response patterns. Our work resolves
the pain point of implementing the anti-sensing idea based on the commercial
off-the-shelf WiFi devices.
