  We revisit the recent secure degrees of freedom (s.d.o.f.) results for
one-hop multi-user wireless networks by considering three fundamental wireless
network structures: Gaussian wiretap channel with helpers, Gaussian multiple
access wiretap channel, and Gaussian interference channel with secrecy
constraints. We present main enabling tools and resulting communication schemes
in an expository manner, along with key insights and design principles emerging
from them. The main achievable schemes are based on real interference
alignment, channel prefixing via cooperative jamming, and structured
signalling. Real interference alignment enables aligning the cooperative
jamming signals together with the message carrying signals at the eavesdroppers
to protect them akin to one-time-pad protecting messages in wired systems. Real
interference alignment also enables decodability at the legitimate receivers by
rendering message carrying and cooperative jamming signals separable, and
simultaneously aligning the cooperative jamming signals in the smallest
possible sub-space. The main converse techniques are based on two key lemmas
which quantify the secrecy penalty by showing that the net effect of an
eavesdropper on the system is that it eliminates one of the independent channel
inputs; and the role of a helper by developing a direct relationship between
the cooperative jamming signal of a helper and the message rate. These two
lemmas when applied according to the unique structure of individual networks
provide tight converses. Finally, we present a blind cooperative jamming scheme
for the helper network with no eavesdropper channel state information at the
transmitters that achieves the same optimal s.d.o.f. as in the case of full
eavesdropper channel state information.
