  Index coding is concerned with efficient broadcast of a set of messages to
receivers in the presence of receiver side information. In this paper, we study
the secure index coding problem with security constraints on the receivers
themselves. That is, for each receiver there is a single legitimate message it
needs to decode and a prohibited message list, none of which should be decoded
by that receiver. To this end, our contributions are threefold. We first
introduce a secure linear coding scheme, which is an extended version of the
fractional local partial clique covering scheme that was originally devised for
non-secure index coding. We then develop two information-theoretic bounds on
the performance of any valid secure index code, namely secure polymatroidal
outer bound (on the capacity region) and secure maximum acyclic induced
subgraph lower bound (on the broadcast rate). The structure of these bounds
leads us to further develop two necessary conditions for a given index coding
problem to be securely feasible (i.e., to have nonzero rates).
