Research On Protocols Of Quantum Information Hiding

With the rapid development of quantum information technology, the outstanding research achievement of quantum secret communication theory and technology has brought a revolutionary impact on the research of the present information science and has aroused great concern. More and more researchers devote themselves to the new scientific research field. It is particularly worth mentioning that information hiding has also been introduced into this remarkable research field. Quantum information hiding, which can be considered as the latest developments of classical information hiding in quantum scenario, employs the effects of quantum information and quantum computation to achieve the target of information hiding by utilizing quantum states as the carriers of information transmission. It is very important in both theoretical significance and practical applications to research quantum information hiding which is a popular topic in quantum information and can be chosen as an alternative method for privacy protection.Combining the basic principle and characteristics of quantum mechanics with the theory and method of classical information hiding, this dissertation researches the key fundamental theory for quantum information hiding and protocols analysis and design for quantum covert channel protocols and quantum steganography protocols based on quantum secure communication which can achieve the unconditional security. Quantum covert channel and quantum steganography are the two important subdisciplines of quantum information hiding protocols, the former establishes covert channels inside the communication channels of quantum secret communication protocols, and the latter embeds messages within other innocuous looking quantum carriers so that the steganographic message is not readable except for the sender and the intended recipient. More details of this work are as follows:(1) This dissertation researches some contents of the key fundamental theory for quantum information hiding. Firstly, we propose the concept of the quantum covert channel, formally introduce the quantum covert channel protocol into the field of quantum information hiding, and classify quantum information hiding into3classes based on the classification method of the classical information hiding. Secondly, in the performance analysis for the proposed quantum information hiding protocols of this dissertation, we research the new connotation of the performance evaluation index for information hiding in the field of quantum information. In particular, to accurately reflect the relationship between the quantum resource consumption and the embedding capacity, we propose a quantitative evaluation index of embedding capacity, named covert communication efficiency. Thirdly, we research the quantum direct communication protocols which support and catalyze the development of quantum information hiding. Based on the two basic properties of Grover search algorithm, we design a deterministic security quantum communication (DSQC) protocol and a quantum secure direct communication (QSDC) protocol.(2) This dissertation focuses on the quantum covert channel based on any QSDC channel which utilizes unitary transformations to encode information. We derive the main idea why a covert channel can be established within any QSDC channel by analyzing the basic properties of the unitary transformations which are used in a QSDC scheme. Because the unitary transformations in a QSDC protocol have three remarkable characteristics:information encoding, secrecy and universality, we can establish another direct communication-channel to transfer secret messages by the unitary transformations used in a given QSDC scheme. And then, a novel quantum covert channel protocol is proposed with unconditional security based on any QSDC channel. The proposed quantum covert channel protocol not only has the same capacity as the given QSDC protocol, but also has the properties of universality and low computation complexity.(3) By the formulas of entanglement swapping of two quantum states, this dissertation deeply researches the type of quantum covert channel protocols based on entanglement swapping. On the one hand, using entanglement swapping of generalized Bell states, we derive a secret message encoding rule and then propose a novel quantum covert channel protocol without consuming any auxiliary quantum state. On the other hand, we point out the defect of the protocol which is based on the entanglement swapping of χ-type states. Because the possible output results of entanglement swapping between a χ-type state and any one of the16different χ-type states can be divided into8groups instead of16groups, it is impossible to encode a4-bit secret message every time in the original protocol. To overcome the defect, an improved quantum covert channel protocol is presented based on the relationship between the input states and the output states of entanglement swapping. This type of quantum covert channel protocols not only has the property of low computation complexity, but also consumes no auxiliary quantum state.(4) To improve the covert communication efficiency, this dissertation proposes a type of quantum covert channel protocol based on the tensor product of multiple two-particle orthorhombic quantum states. Based on the tensor product of two Bell states, we propose a secret message encoding rule and then propose a generalized high-efficiency quantum covert channel protocol. To further improve the embedding capacity, we generalize this protocol and propose a type of quantum covert channel protocol based on the tensor product of multiple two-particle orthorhombic quantum states. This type of quantum covert channel protocol not only consumes no auxiliary quantum state, but also has low computation complexity and good universality.(5) This dissertation analyzes and improves a quantum steganography protocol which is based on GHZ4state. Since all of the8groups of unitary transformations used in the original protocol change the GHZ4state into6instead of8different quantum states when the global phase is not considered, we point out that a2-bit instead of a3-bit secret message can be encoded by one group of the given unitary transformations. To encode a3-bit secret message by performing a group of unitary transformations on the GHZ4state, we give another8groups of unitary transformations that can change the GHZ4state into8different quantum states.