Continuous-variable quantum cryptography with an untrusted relay: detailed security analysis of the symmetric configuration

TY - JOUR

T1 - Continuous-variable quantum cryptography with an untrusted relay

T2 - detailed security analysis of the symmetric configuration

AU - Ottaviani, Carlo

AU - Spedalieri, Gae

AU - Braunstein, Samuel Leon

AU - Pirandola, Stefano

PY - 2015/2/18

Y1 - 2015/2/18

N2 - We consider the continuous-variable protocol of Pirandola et al. [Nature Photonics 9, 397-402 (2015), see also arXiv.1312.4104] where the secret key is established by the measurement of an untrusted relay. In this network protocol, two authorized parties are connected to an untrusted relay by insecure quantum links. Secret correlations are generated by a continuous-variable Bell detection performed on incoming coherent states. In the present work we provide a detailed study of the symmetric configuration, where the relay is midway between the parties. We analyze symmetric eavesdropping strategies against the quantum links explicitly showing that, at fixed transmissivity and thermal noise, two-mode coherent attacks are optimal, manifestly outperforming one-mode collective attacks based on independent entangling cloners. Such an advantage is shown both in terms of security threshold and secret-key rate.

AB - We consider the continuous-variable protocol of Pirandola et al. [Nature Photonics 9, 397-402 (2015), see also arXiv.1312.4104] where the secret key is established by the measurement of an untrusted relay. In this network protocol, two authorized parties are connected to an untrusted relay by insecure quantum links. Secret correlations are generated by a continuous-variable Bell detection performed on incoming coherent states. In the present work we provide a detailed study of the symmetric configuration, where the relay is midway between the parties. We analyze symmetric eavesdropping strategies against the quantum links explicitly showing that, at fixed transmissivity and thermal noise, two-mode coherent attacks are optimal, manifestly outperforming one-mode collective attacks based on independent entangling cloners. Such an advantage is shown both in terms of security threshold and secret-key rate.

KW - quant-ph

KW - physics.optics

U2 - 10.1103/PhysRevA.91.022320

DO - 10.1103/PhysRevA.91.022320

M3 - Article

SN - 1050-2947

VL - 91

JO - Physical Review A

JF - Physical Review A

IS - 2

M1 - 022320

ER -