  The cognitive interference channel with confidential messages (CICC) proposed
by Liang et. al. is investigated. When the security is considered in coding
systems, it is well known that the sender needs to use a stochastic encoding to
avoid the information about the transmitted confidential message to be leaked
to an eavesdropper. For the CICC, the trade-off between the rate of the random
number to realize the stochastic encoding and the communication rates is
investigated, and the optimal trade-off is completely characterized.
