Analysis of an attenuator artifact in an experimental attack by Gunn-Allison-Abbott against the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange system
This work addresses a security concern for quantum-resistant key exchange systems, but it is incremental as it corrects a specific experimental error rather than advancing the field broadly.
The authors refute a prior claim that the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange system has a severe information leak, demonstrating that the claim resulted from a design flaw involving an attenuator that broke the system's essential single Kirchhoff-loop, and they crack the flawed scheme with an elementary current comparison attack yielding negligible error probability.
A recent paper by Gunn-Allison-Abbott (GAA) [L.J. Gunn et al., Scientific Reports 4 (2014) 6461] argued that the Kirchhoff-law-Johnson-noise (KLJN) secure key exchange system could experience a severe information leak. Here we refute their results and demonstrate that GAA's arguments ensue from a serious design flaw in their system. Specifically, an attenuator broke the single Kirchhoff-loop into two coupled loops, which is an incorrect operation since the single loop is essential for the security in the KLJN system, and hence GAA's asserted information leak is trivial. Another consequence is that a fully defended KLJN system would not be able to function due to its built-in current-comparison defense against active (invasive) attacks. In this paper we crack GAA's scheme via an elementary current comparison attack which yields negligible error probability for Eve even without averaging over the correlation time of the noise.