  Based on the detection loophole-free photon key distribution (PKD) compatible
with classical optical systems, an optical key distribution (OKD) protocol is
presented for unconditionally secured cryptography in fiber-optic
communications networks using addressable continuous phase basis, where each
communication channel is composed of paired transmission lines. The
unconditional security in OKD lies in quantum superposition between the paired
lines of each channel. The continuous phase basis in OKD can be applied for
one-time-pad optical cryptography in networks, whose network address capacity
is dependent upon the robustness of OKD to channel noises.
