  The security of the Kirchhoff-law-Johnson-(like)-noise (KLJN) key exchange
system is based on the Fluctuation-Dissipation-Theorem of classical statistical
physics. Similarly to quantum key distribution, in practical situations, due to
the non-idealities of the building elements, there is a small information leak,
which can be mitigated by privacy amplification or other techniques so that the
unconditional (information theoretic) security is preserved. In this paper, the
industrial cable and circuit simulator LTSPICE is used to validate the
information leak due to one of the non-idealities in KLJN, the parasitic
(cable) capacitance. Simulation results show that privacy amplification and/or
capacitor killer (capacitance compensation) arrangements can effectively
eliminate the leak.
