The motivation for this study about Physical Layer Security comes from bridging the gap between the vast theory and a feasible implementation. We propose a Physical-Layer-Security Box as a system-level Box is a system-level solution, named PLS-Box, to solve the key exchange between two wireless communicating parties. The PLS-Box performs a novel key generation method named time-frequency filter-bank. The entropy of the radio channel is harvested via a filter-bank processing, and then turned into a reciprocal security key, at both ends. In this concept work, we also focus on several PLS open issues, such as radio-frequency imperfections and accessibility to the baseband communication modem. The goal is to show a wide applicability of our PLS-Box to actual wireless systems, paving the way for an evolution of existing schemes.