Response to Feng Hao's paper "Kish's key exchange scheme is insecure"

Abstract

In a forthcoming paper in IEE Proceedings Information Security, Feng Hao claims that temperature inaccuracies make the key exchange scheme based on Kirchhoff Loop with Johnson-like Noise insecure. First we point out that this claim is irrelevant for the security of the idealized/mathematical communicator because it violates basic assumptions. Furthermore, in general practical applications, as it has been pointed out in the very first paper, the use of thermal noise is disadvantageous therefore the issue of temperature and its accuracy is unimportant even for the security of common practical realizations. It is important to emphasize that any deviation from the idealized scheme can lead to a finite level of security. Thus, if the above-mentioned author had stressed the inaccuracy of the resistor values; his claim would have been practically valid. However the impact of such systematic errors can be kept under control. Here we cite our relevant analysis (Phys. Lett. A 359, (2006) 741-744) of 1% voltage inaccuracy along the line due to wire resistance effects, which can be considered as a general result for inaccuracies of this order. The necessity to build a statistics to extract information during the properly chosen clock time leads to extremely poor eavesdropper statistics and this situation provides a good practical raw bit security that can be orders of magnitude beyond the raw bit security of idealized quantum communicators.