We address the efficiency and robustness of quantum key distribution (QKD) based on entangled states in conditions of noisy quantum channels. We consider schemes based on either source or detection station located in the middle or the channel, the latter configuration allowing realization of measurement-device independent QKD. In our study we focus both on discrete-variable (DV) QKD protocols utilizing direct photodetection as well as continuous-variable (CV) ones, which are based on the homodyne detection. Equivalently parametrizing the channel excess noise for both DV and CV protocols, we use robustness of an ideal CV QKD protocol as a benchmark for the entanglement-based DV QKD. We show that DV protocols typically overcome the CV ones in both source- and detector-in-the-middle setup configurations. However, this advantage can be undermined by the practical aspects on the DV protocols. Considering quantum-dot type of the DV sources of entanglement, we show the levels of pair generation and collection efficiencies needed to overcome any CV protocols. The requirements are generally compatible with the existing technologies but may require experimental efforts to achieve. Our results are essential for the practical entanglement-based QKD protocols with modern efficient sources, aimed at potential scalability in the quantum networks.
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