  Using a broadcast channel to transmit clients' data requests may impose
privacy risks. In this paper, we address such privacy concerns in the index
coding framework. We show how a malicious client can infer some information
about the requests and side information of other clients by learning the
encoding matrix used by the server. We propose an information-theoretic metric
to measure the level of privacy and show how encoding matrices can be designed
to achieve specific privacy guarantees. We then consider a special scenario for
which we design a transmission scheme and derive the achieved levels of privacy
in closed-form. We also derive upper bounds and we compare them to the levels
of privacy achieved by our scheme, highlighting that an inherent trade-off
exists between protecting privacy of the request and of the side information of
the clients.
