Multi-Party Semi-Quantum Key Agreement Protocol And Its Security

The rapid development of quantum algorithms and quantum computer technology has brought a great threat to most of the traditional key systems that rely on computational complexity to ensure security.The quantum key agreement protocol does not rely on mathematical computational complexity to ensure its security,and carries key information with qubits.Once the eavesdrop operations are detected during the transmission of qubits,the protocol will be terminated directly.The quantum key agreement protocol can resist the attacks with full quantum capabilities and ensure unconditionally security in the sense of the information theory.Moreover,the application of the semi-quantum concept in quantum cryptography reduces the technical cost of the quantum communication effectively and promotes the practical application of quantum key agreement protocol.A multi-party semi-quantum key agreement protocol based on four-particle Cluster state and two multi-party semi-quantum key agreement protocols that can resist collective noise were proposed.The main work of this dissertation is as follows:A multi-party semi-quantum key agreement protocol was proposed based on delegating private quantum computation with the four-qubit Cluster states,and the correctness of the protocol was proved.Participants in the protocol only need to have the ability to reorder particles,prepare and measure qubits under the computing basis.Participants delegate the unitary operations on encoded particles to the untrusted quantum center and obtain the final consensus shared secret with the help of the quantum center.By randomly inserting confusion states into the encoding particle sequences,the proposed protocol can defend the eavesdropping attack from the quantum center.Since the quantum center does not perform joint measurement until all participants have completed the N rounds of encoding processes,the fairness of the proposed protocol is guaranteed.Because of the inserted decoy states,the proposed protocol is immune to measurement retransmission attack,interception retransmission attack,entangle-measure attack,and modification attack.Due to the dense coding methods,the qubit efficiency of the proposed multi-party semi-quantum key agreement protocol is higher than those of most existing multi-party quantum key agreement protocols when more than five participants are involved.On the basis of the proposed multi-party semi-quantum key agreement protocol,the four-particle Cluster state was replaced by the corresponding six-particle logical state.Two multi-party semi-quantum key agreement protocols that can resist collective noise were designed.The initiator of the protocol does not delegate the quantum center to perform encoding operations on the encoding particle sequences according to his own private key,and the quantum center cannot obtain his private key.Therefore,the proposed protocol can resist eavesdropping attacks from the quantum center.When the quantum center completes a round of encoding operations,the quantum center will perform the CNOT gate and the H gate to these six-particle logical states.Since the quantum center does not perform joint measurement until all participants have completed N rounds of the encoding processes,the two proposed protocols are fair to all participants.Furthermore,the proposed protocol is also immune to common outsider attacks due to the logical decoy states in the protocol.With the help of the super dense coding method,the qubit efficiency of the two proposed protocols can be improved.