The Design And Analysis Of Quantum Secure Direct Communication Protocol

In the 80s of the last century, Bennett, together with some other people, put forward the concept of quantum cryptography, and the first protocol of quantum key distribution(QKD)--BB84, which inaugurated the new era of quantum cryptography. Quantum cryptography is the combination of classic cryptography and quantum mechanics, and its security, which relies on the basic principle of quantum mechanics, is different from the classic cryptography system based on mathematics. In 2000, Shor gave the proof of the unconditional security about the BB84 protocol. On the aspect of security, quantum cryptography brought a new idea to the field of cryptography. Quantum cryptography provides new theories and methods to the research on modern cryptography, which will have great effect on the national information security. In order to adapt to the speedy development of information science, the exploration and research of the high-security quantum cryptography and taking position of its high point have become the important subject which attracts great attention of the world.People proposed quantum secure direct communication(QSDC) after presenting the idea of QKD. The application in communication field of QKD requires that the two parties share the classic key by QKD in advance, and then they communicate with each other by one-time-pad system to encrypt and decrypt secret messages. Different from QKD, QSDC does not need the process of QKD, two parties can transfer the secret message directly using the basic principle of quantum mechanics and the eavesdropper will gain nothing of the secret message. QSDC can be applied in which communicating parties don't share keys.This paper mainly focuses on the designing methods and security analysis of QSDC. The introduction of chapter 1 mainly talks about the research background and significance of QSDC, the current research status and development, and in the last it presents the dissertation's arrangement and main research result.Chapter 2 mainly introduces the basic knowledge of quantum machanics, which is needed in the research of QSDC. It includes the basic axioms of quantum machanics, Heisenberg uncertainty principle, quantum no-cloning theorem, quantum entanglement and so on. In addition it elaborates the basic knowledge of quantum cryptography including the BB84 protocol, the incoherent attack and so on.In chapter 3, it puts forward two QSDC schemes respectively based on GHZ and W state. The first scheme takes GHZ state as the information carrier, using the CNOT gate to encode without transferring the quantum bit containing secret message. With local measurement and classic communication, it can securely transfer secret message simultaneously from two sides to the third party. The second scheme takes the ordered four-particle W state as the information carrier, using unitary permutation to encode and directly transfers secret message by local Bell base measurement and classic communication. In the ideal channel, two schemes are secure against the common incoherent attacking strategies.Chapter 4 represents two QSDC schemes with authentication based on partially entangled state. The first one takes three-particle partially entangled state as information carrier, using quantum entanglement swapping, so that the transfer of quantum state is needed only once and there is no need to transmit quantum bits with secret message in the channel. It transfers secret message simultaneously from two sides to the third party using local measurement and classic communication. The second one uses three-particle partially entangled state and CNOT gate to encode and decode the secret message. In the scheme, two sides can transfer secret message to the third party simultaneously, and the shared partially entangled state can be used repeatedly. The two schemes are secure under the incoherent attack in the ideal channel.