  We analyze a two-receiver binary-input discrete memoryless broadcast channel,
in which the transmitter communicates a common message simultaneously to both
receivers and a covert message to only one of them. The unintended recipient of
the covert message is treated as an adversary who attempts to detect the covert
transmission. This model captures the problem of embedding covert messages in
an innocent codebook and generalizes previous covert communication models in
which the innocent behavior corresponds to the absence of communication between
legitimate users. We identify the exact asymptotic behavior of the number of
covert bits that can be transmitted when the rate of the innocent codebook is
close to the capacity of the channel to the adversary. Our results also
identify the dependence of the number of covert bits on the channel parameters
and the characteristics of the innocent codebook.
