  A broadcast channel (BC) where the decoders cooperate via a one-sided link is
considered. One common and two private messages are transmitted and the private
message to the cooperative user should be kept secret from the
cooperation-aided user. The secrecy level is measured in terms of strong
secrecy, i.e., a vanishing information leakage. An inner bound on the capacity
region is derived by using a channel-resolvability-based code that double-bins
the codebook of the secret message, and by using a likelihood encoder to choose
the transmitted codeword. The inner bound is shown to be tight for
semi-deterministic and physically degraded BCs and the results are compared to
those of the corresponding BCs without a secrecy constraint. Blackwell and
Gaussian BC examples illustrate the impact of secrecy on the rate regions.
Unlike the case without secrecy, where sharing information about both private
messages via the cooperative link is optimal, our protocol conveys parts of the
common and non-confidential messages only. This restriction reduces the
transmission rates more than the usual rate loss due to secrecy requirements.
An example that illustrates this loss is provided.
