Research On Theories And Schemes Of Quantum Secure Communication

Quantum information science, which mainly consists of quantum communications and quantum computing, has been developed quickly to be one of the newest cross-linked research fields. With the development of quantum computing, traditional crypto-systems for communications are no longer secure. However, quantum communication with unconditional security on basis of quantum mechanics, for which it is impossible to be attacked by the infinite increasingly computation ability, provides a new idea and approach for information security transmissions. In the meantime, it is also a method to ensure information security communication as soon as quantum computers appear successfully in the future. Since the first quantum key distribution (QKD) protocol-BB84 was proposed in 1984, much progress has been made in both of theoretical investigations and experimental implements. However, quantum secure communication standards haven't been formed; and some schemes also need further improvement. Based on the classical information theory and quantum mechanics, this dissertation focuses on some theoretical issues and schemes of quantum secure communication for actual application and safety, in particular, mainly researches into communication protocol analysis, quantum secure direct communication, quantum secret sharing, quantum network communication, quantum channel coding and so on. Main contributions are summarized as follows:(1) A quantum coding attack strategy is proposed to attack the "ping-pong" communication protocol. Based on theories and techniques of the stabilizer quantum error correction code, attacking strategies of "Ping-Pong" scheme based on either entanglement state or no orthogonal state are proofed and demonstrated, respectively. Furthermore, information obtained by Eve and the possible probability detected by the legitimate communicators are analyzed by employing information theory. Finnally, three kinds of schemes are proposed to withstand the presented coding attacking strategies.(2) Three kinds of quantum secure direct communication schemes are presented. The first scheme is proposed to exchange directly the communicators'secret messages by making use of entanglement swapping of Bell states and super dense coding. It has great capacity to distribute the secret messages to each other since these messages have been imposed on high-dimensional Bell states via the local unitary operations with super dense coding. The security is ensured by the secure transmission of the travelling sequences and the application of entanglement swapping. Secondly, considering entanglement state is more difficult in preparing and detecting than single photons without correlation. Based on single photons with random polarization angel, a deterministic secure bidirectional or single diretional quantum communication scheme is presented. In this scheme, secret messages are encoded in the single photons rotated random polarization angle by performing a series of independent operations in three-way quantum channel. This scheme, which is similar to traditional communication mode, is more suitable for the practical communication. Thirdly, a quantum secure direct communication protocol based on chaos is proposed with authentication. Identity verification is flexibly combined with the general Arnold map in this scheme, and identity authentication and deterministic message transmission are completed simultaneously in a one-way channel. Direct message transmission is based on the secret order of transmission particles, and the secret order relies on a chaotic map with the essence of cryptographic security. Identity verification and the key of the general Arnold map depend on the correlation of the shared EPR pairs using Bell's theorem. The shared EPR pairs and the key are used only once, as in the secure one-time pad protocol. Furthermore, our scheme also improves the practical applicability of quantum direct communication compared with the convensional QSDC schemes.(3) A (n,n)-threshold scheme of multiparty quantum secret sharing of classical or quantum message is proposed based on the discrete quantum Fourier transform (QFT). In fact, it is a multiparty quantum key distribution. In our proposed scheme, the secret messages, which are encoded by using the forward quantum Fourier transform and decoded by using the reverse, are split and shared in such a way that it can be reconstructed among them only if all the participants work in concert. Furthermore, we also discuss how this protocol must be carefully designed for correcting errors and checking eavesdropping or a dishonest participant. Security analysis shows that our scheme is secure. Also, this scheme has an advantage that it is completely compatible with quantum computation and easier to be realized in the distributed quantum secure computation. A deterministic one-step quantum key distribution scheme based on QFT is also proposed. In the proposed scheme, the secret key, which is encoded and decoded by using QFT, is deterministic. The whole process only needs a step communication. Moreover, it has an advantage of not exchanging any other classical information except for eavesdropping check.(4) A quantum network communication scheme via multi-step quantum teleportation is proposed in a small-scale network based on entanglement of Bell states. In this scheme, it contains certain number of single-qubit quantum source nodes that teleport unknown quantum states to other nodes on the network in the multi-teleport fashion where every intermediate node can pass on any of its received quantum information to others via multi-step quantum teleportation. This scheme is implemented for quantum network communication with two phases, i.e., the phase for executing teleportation of unknown single-qubit states and the phase for teleportation of combined unknown two-qubit states. Advantages of our scheme lie in Synchronous communications among multi-points and its linearity, which is easy to implement for quantum communications in practical applications. In addition, this scheme is secure since the process of quantum teleportation is based on entanglement of Bell states which has been securely set up in advance as quantum channels.(5) A kind of stabilizer quantum code is proposed based on multilevel constructed matrices. The N-k generators of the stabilizer of the designed codes [[N, k, d]]can be constructed via selecting randomly N-k rows from a concatenated matrix with the orthogonal rows. Thus, it is very easy to construct these kinds of codes with arbitrary larger N, and breakthroughs the present bound on the minimum distance for codeword length N up to 30 qubits. Furthermore, the resulting codes with better perimeters are more efficient than the previous quantum codes. A quantum polarization coding scheme with Quantum-CNOT Operations is also suggested to design quantum bit (qubit) sequences that achieve the symmetric capacity for any given binary-input discrete memoryless quantum channels. Quantum channel polarization is proposed as a quantum coding technique to construct a quantum polar code for quantum transmissions with much efficiency. We have boosted the symmetric capacity to near channel capacity. Moreover, its coding and decoding complexity is much lower with the recurisive decoding algorithms.