Resource-efficient energy test and parameter estimation in continuous-variable quantum key distribution

Symmetry plays a fundamental role in the security analysis of quantum key distribution (QKD). Here we review how symmetry is exploited in continuous-variable (CV) QKD to prove the optimality of Gaussian attacks in the finite-size regime. We then apply these results to improve the feasibility and the key rate of these protocols. First we show how to improve the feasibility of the energy test, which is one important routine aimed at establishing an upper bound on the effective dimensions of the otherwise infinite-dimensional Hilbert space of CV systems. Second, we show how the routine of parameter estimation can be made resource efficient in measurement-device independent QKD. These results show that all the raw data can be used both for key extraction and for the routines of the energy test and parameter estimation. Furthermore, the improved energy test does not require active symmetrization of the measured data, which is computationally demanding.