A theoretical and experimental test on the security of quantum cryptography key distribution Ekert's protocol based on Wigner's inequality
Stefania Castelletto, Ivo Pietro Degiovanni, Maria Luisa Rastello, Ivano Ruo Berchera, Fabio Antonio Bovino, A.M. Colla, Giuseppe Castagnoli · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2004
In this paper we prove both theoretically and experimentally the insecurity of the Ekert’s protocol for quantum-key distribution when based on the Wigner inequality when entangled photon pairs are used as source. The security proof of the Eckert’s protocol based on Wigner’s inequality consists in verifying the violation of W ≥ 0 (which corresponds to local-realistic theories). We highlight that a violation of the Wigner’s inequality occurs when Eve controls the two quantum channels. We give the theoretical motivation for this result and we perform an experiment proving this weakness, by realizing the condition of Eve gaining total control of the source of photon pairs. In addition we calculate the modified version of this inequality which guarantees safe quantum-key distribution, thus proving it experimentally.