Eavesdropper's Optimal Information in Variations of Bennett-Brassard 1984 Quantum Key Distribution in the Coherent Attacks

We calculate eavesdropper's optimal information on raw bits in Bennett-Brassard 1984 quantum key distribution (BB84 QKD) and six-state scheme in coherent attacks, using a formula by Lo and Chau [Science 283 (1999) 2050] with single photon assumption. We find that eavesdropper's optimal information in QKD without public announcement of bases [Phys. Lett. A 244 (1998) 489] is the same as that of a corresponding QKD WITH it in the coherent attack. We observe a sum-rule concerning each party's information.