  This paper starts by assuming a 1-2-1 network, the abstracted noiseless model
of mmWave networks that was shown to closely approximate the Gaussian capacity
in [1], and studies secure communication. First, the secure capacity is derived
for 1-2-1 networks where a source is connected to a destination through a
network of unit capacity links. Then, lower and upper bounds on the secure
capacity are derived for the case when source and destination have more than
one beam, which allow them to transmit and receive in multiple directions at a
time. Finally, secure capacity results are presented for diamond 1-2-1 networks
when edges have different capacities.
