  In this paper we determine the noise properties needed for unconditional
security for the ideal Kirchhoff-Law-Johnson-Noise (KLJN) secure key
distribution system using simple statistical analysis. It has already been
shown using physical laws that resistors and Johnson-like noise sources provide
unconditional security. However real implementations use artificial noise
generators, therefore it is a question if other kind of noise sources and
resistor values could be used as well. We answer this question and in the same
time we provide a theoretical basis to analyze real systems as well.
