| Quantum cryptography is a new technology which gets a high level of attention todayworldwide. Unlike traditional classical cryptography based on various mathematical tech-niques, quantum cryptography can realize the unconditionally secure communication andinformation protection, in which the security is only guaranteed by the fundamental lawsof quantum mechanics, i.e., Heisenberg’s uncertainty principle and quantum no-cloningtheorem. Quantum cryptography has developed very quickly and obtained signifcantachievements in theory and experiments. The content of this dissertation includes quan-tum key agreement, quantum secure direct communication, and quantum signature. Thedetails are as follows:(1) We propose a three-party quantum key agreement with Bell states. A key agreementbased on the quantum efects can satisfy not only the security of quantum keydistribution but also the fairness. In this protocol the three parties are entirely peerand each one has an equal contribution to the shared secret key. Each party sendsthe particle sequences to the other parties respectively and measurements theseencoded sequences after receiving them. From this kind of bidirectional circuit ofqubit transmission, the shared key can be established by extracting each party’ssecret key.(2) In a unidirectional qubit circuit, we propose a three-party quantum key agreementwith two-qubit entanglement. Compared with the bidirectional qubit circuit, thispattern results in a simpler protocol implementation and achieve higher efciency.This scheme can establish a session key in the insecure channel and the shared keycannot be determined by any one or two of them. This protocol can resist theoutsider attack and the insider attack.(3) By using the idea of quantum dense coding, we propose an efcient protocol for bidi-rectional quantum secure communication with two-photon entanglement. We frstfnd two nonorthogonal measurement bases and the users exchange their messagesthrough unitary operations and Bell measurement. Compared with the scheme pro-posed by Shi et al, the entangled pairs are chosen randomly and the number of bothquantum resources and bits in a classical channel is a half. Moreover, our protocolcan achieve higher efciency. The secure analysis shows information leakage doesnot exist in our scheme.(4) We propose an efcient three-party quantum secure direct communication basedon EPR pairs. We point out the security hole, which the eavesdropper can obtain the correlation of secret messages exchanged by the users from the public classicalchannel. By improving the quantum channel and classical channel, our scheme canavoid this kind of drawback, in which the entangled states can encode longer secretmessages. In addition, our protocol increases efciency.(5) We propose a quantum proxy group signature with four-qubit entangled states.This scheme combines the properties of group signature and proxy signature andhas some features including unforgeability, verifability, identifability, undeniability,and group property. The particle sequences can be used to distribute proxy warrantsand secret keys based on quantum secure direct communication, and then can beused for signing and verifcation processes. Thus our protocol raises the utilizationrate of quantum resources. The outside attack and participant attack are alsoanalyzed.(6) A quantum blind signature scheme is proposed, which can be applied to E-votingsystem. In this protocol, the voter can blind his message at frst, and obtain theblind signature from the electoral management center. Finally, this signature isverifed. The signatory knows nothing about the content that he signed and themessage could be protected to ensure privacy. Moreover, our protocol can performan audit program with respect of the validity of the verifcation process in the lightof actual requirements. |
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