It has been shown recently that the use of two pairs of resistors with enhanced Johnson-noise and a Kirchhoff-loop-i.e., a Kirchhoff-Law-Johnson-Noise (KLJN) protocol-for secure key distribution leads to information theoretic security levels superior to those of a quantum key distribution, including a natural immunity against a man-in-the-middle attack.
http://arxiv.org/abs/1206.2534I'll admit some of this goes over my head but I'm curious as to what our resident physicists think. Is this type of cryptography based on the second law of thermodynamics really harder to break than that based on quantum mechanics?