Quantum Cryptography Protocols Robust against Photon Number Splitting Attacks for Weak Laser Pulse Implementations

We introduce a new class of quantum key distribution protocols, tailored to be robust against photon number splitting (PNS) attacks. We study one of these protocols, which differs from the original protocol by Bennett and Brassard (BB84) only in the classical sifting procedure. This protocol is provably better than BB84 against PNS attacks at zero error.

Figure 1

Two pairs of nonorthogonal states on the equator of the Poincaré sphere, and the effect of the filter $F_{\mathcal{A}}$.

Figure 2

PNS attacks with $\mathrm{Q}\mathrm{B}\mathrm{E}\mathrm{R}=0$ on the BB84 protocol for $\mu =0.1$ and on the new protocol for $\mu =0.2$: Eve’s information as a function of the attenuation $\delta =\alpha \ell$.