In this talk, we consider the relay network where an eavesdropper is
co-located with the relay node. This model exemplifies a practical
cooperation scenario where the help of a relay node may be enlisted
despite it being "untrustworthy", and hence the information must be
kept secret from the relay. We describe an achievable secrecy rate
based on compress-and-forward, as well as an upper bound on the
secrecy rate. We focus on two specific models of this relay network
with orthogonal components. For model one, we find its secrecy
capacity and prove the relay is not useful. For model two, we show the
relay can be very useful despite it being treated as the eavesdropper,
and provide an example where the relay helps improve an otherwise-zero
secrecy rate. We then proceed to assess the value of the upper bound
for this model, and show two channel models in which the bound is
tight asymptotically, and exactly, respectively. The latter thus
provides an example where the secrecy capacity is attained via the
compress-and-forward scheme.