Robustness of the round-robin differential-phase-shift quantum-key-distribution protocol against source flaws

Recently, a new type of quantum key distribution, called the round-robin differential-phase-shift (RRDPS) protocol [T. Sasaki et al., Nature (London) 509, 475 (2014)], was proposed, where the security can be guaranteed without monitoring any statistics. In this Rapid Communication, we investigate source imperfections and side-channel attacks on the source of this protocol. We show that only three assumptions are needed for the security, and no detailed characterizations of the source or the side-channel attacks are needed. This high robustness is another striking advantage of the RRDPS protocol over other protocols.

Figure 1

Secret key rate $R$ per pulse versus distances $l$. The solid line is for case (i): $p_0^{\left(k\right)}\left(0\right)=p_1^{\left(k\right)}\left(0\right)$ is satisfied for all $k$, and the dashed line is for case (ii): $p_0^{\left(k\right)}\left(0\right)\ne p_1^{\left(k\right)}\left(0\right)$ occurs for some or every $k$.