For Reusable Key Communication Attacks And Security Improvements Program

In the papers [Phys. Rev. A 64, 024302 (2001)] and [Phys. Pev. A 67, 044302(2003)], the authors proposed a protocol for secure communication withquantum key encryption, respectively. Because these quantum keys can be reused, a lot of quantum sources are saved and the efficiency of communication is alsoimproved. These works inspire a new perspective for quantum communication, Inthis paper, we study the two novel protocols and show a kind of attacking strategythat a potential eavesdropper can eavesdrop the whole secret information using twoancillary qubits without being detected. Thus we propose a modified quantumsecret sharing protocol in which the sender randomly chooses single qubits or EPRpairs as information carriers to ensure the security of communication. In everyround the legitimated users must cooperate to gain the secret information, and theeavesdropping behavior of eavesdropper can be detected by the legitimated users.Furthermore, the efficiency of information sharing can be increased. We hope thatour discussion can be helpful for the improving of the protocols mentioned above.