  In this paper, the $K$-user interference channel with secrecy constraints is
considered with delayed channel state information at transmitters (CSIT). We
propose a novel secure retrospective interference alignment scheme in which the
transmitters carefully mix information symbols with artificial noises to ensure
confidentiality. Achieving positive secure degrees of freedom (SDoF) is
challenging due to the delayed nature of CSIT, and the distributed nature of
the transmitters. Our scheme works over two phases: phase one in which each
transmitter sends information symbols mixed with artificial noises, and repeats
such transmission over multiple rounds. In the next phase, each transmitter
uses delayed CSIT of the previous phase and sends a function of the net
interference and artificial noises (generated in previous phase), which is
simultaneously useful for all receivers. These phases are designed to ensure
the decodability of the desired messages while satisfying the secrecy
constraints. We present our achievable scheme for three models, namely: 1)
$K$-user interference channel with confidential messages (IC-CM), and we show
that $\frac{1}{2} (\sqrt{K} -6) $ SDoF is achievable, 2) $K$-user interference
channel with an external eavesdropper (IC-EE), and 3) $K$-user IC with
confidential messages and an external eavesdropper (IC-CM-EE). We show that for
the $K$-user IC-EE, $\frac{1}{2} (\sqrt{K} -3) $ SDoF is achievable, and for
the $K$-user IC-CM-EE, $\frac{1}{2} (\sqrt{K} -6) $ is achievable. To the best
of our knowledge, this is the first result on the $K$-user interference channel
with secrecy constrained models and delayed CSIT that achieves a SDoF which
scales with $K$, the number of users.
