Quantum Information Processing

, Volume 13, Issue 10, pp 2213–2219 | Cite as

On the security of the Kirchhoff-law–Johnson-noise (KLJN) communicator

  • Laszlo B. Kish
  • Claes G. Granqvist


A simple and general proof is given for the information theoretic (unconditional) security of the Kirchhoff-law–Johnson-noise key exchange system under practical conditions. The unconditional security for ideal circumstances, which is based on the second law of thermodynamics, is found to prevail even under slightly non-ideal conditions. This security level is guaranteed by the continuity of functions describing classical physical linear, as well as stable non-linear, systems. Even without privacy amplification, Eve’s probability for successful bit guessing is found to converge toward 0.5—i.e., the perfect security level—when ideal conditions are approached.


Classical physical secure key exchange Johnson noise 



L.K. is grateful to Horace Yuen, Vadim Makarov, Vincent Poor, and Renato Renner for helpful discussions about relevant security measures.


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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  1. 1.Department of Electrical and Computer EngineeringTexas A&M UniversityCollege StationUSA
  2. 2.Department of Engineering Sciences, The Ångström LaboratoryUppsala UniversityUppsalaSweden

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