ANALYZING AND REVISING A TWO-WAY PROTOCOL FOR QUANTUM CRYPTOGRAPHY WITH A NONMAXIMALLY ENTANGLED QUBIT PAIR
The security of the second (STF-B) protocol of quantum cryptography proposed by Shimizu, Tamaki and Fukasaka (STF) [Phys. Rev. A 80 (2009) 022323] is analyzed in a general way, which shows that the STF-B protocol is vulnerable under a kind of generalized attack. Sufficient and necessary condition for which Eve can successfully attack the message M without introducing errors is deduced. It shows that the correlation-elicitation (CE) attack strategy found by Qin et al. [Phys. Rev. A 82 (2010) 036301] is a special case of the sufficient and necessary condition. Next, we advance an effective and efficient strategy to prevent the general attack. Hence, the STF-B protocol is revised to a secure one by improving the control mode.
quantum key distribution nonmaximally entangled state security analysis