  This paper derives outer bounds on the secrecy capacity region of the 2-user
Z interference channel (Z-IC) with rate-limited unidirectional cooperation
between the transmitters. First, the model is studied under the linear
deterministic setting. The derivation of the outer bounds on the secrecy
capacity region involves careful selection of the side information to be
provided to the receivers and using the secrecy constraints at the receivers in
a judicious manner. To this end, a novel partitioning of the encoded messages
and outputs is proposed for the deterministic model based on the strength of
interference and signal. The obtained outer bounds are shown to be tight using
the achievable scheme derived by the authors in a previous work. Using the
insight obtained from the deterministic model, outer bounds on the secrecy
capacity region of the 2-user Gaussian Z-IC are obtained. The equivalence
between the outer bounds for both the models is also established. It is also
shown that secrecy constraint at the receiver does not hurt the capacity region
of the 2-user Z-IC for the deterministic model in the weak/moderate
interference regime. On the other hand, the outer bounds developed for the
Gaussian case shows that secrecy constraint at the receiver can reduce the
capacity region for the weak/moderate interference regime. The study of the
relative performance of these bounds reveals insight into the fundamental
limits of the 2-user Z-IC with limited rate transmitter cooperation.
