A semi-quantum key distribution method and system suitable for hybrid networking

Abstract

This application discloses a semi-quantum key distribution method and system suitable for hybrid networking, relating to the field of key distribution. The method includes: determining the node state in the hybrid network; the node state being either trusted or untrusted; if the node state is trusted, the nodes in the hybrid network use a one-way code-based semi-quantum key distribution protocol for key distribution; if the node state is untrusted, the nodes in the hybrid network use a dual-field semi-quantum key distribution protocol for key distribution; the nodes in the hybrid network include one quantum side and two classical sides; the one-way code-based semi-quantum key distribution protocol distributes the key to the two classical sides in the quantum direction; the dual-field semi-quantum key distribution protocol sends a coherent state or a vacuum state to the quantum side in the two classical directions, and the two classical sides obtain the key based on a valid event without interference. This application can meet the application needs of different scenarios and improves the key rate and security in semi-quantum communication.

Description

Technical Field

[0001] This application relates to the field of key distribution, and in particular to a semi-quantum key distribution method and system suitable for hybrid networking. Background Technology

[0002] Quantum Key Distribution (QKD) technology primarily utilizes the principles of quantum mechanics for information transmission and encryption, and is considered crucial for future secure information transmission. However, the application prospects of QKD protocols are still limited by hardware infrastructure, especially as the number of users increases, the complexity of network structures and the difficulty of users sharing parameters such as reference frames rise dramatically.

[0003] Semi-quantum key distribution (SQKD) is a quantum cryptography technique that enables secure key exchange even when one party is a quantum party and the other a classical party (who can only prepare or measure quantum states using a set of basis vectors). Its core advantages over QKD are: in semi-quantum communication, even if the classical party cannot fully prepare or measure quantum states, unconditional secure key exchange in an information-theoretic sense can still be achieved through a specific protocol; and the classical party does not require complex quantum devices, reducing network access costs and technical barriers, making quantum communication more accessible.

[0004] Despite the progress made in SQKD technology, several key technical challenges still hinder its practical application and development. One issue is security. Device defects, modulation errors, and environmental interference can lead to eavesdropping. For example, Trojan horse attacks are a serious security vulnerability in bidirectional QKD systems, and SQKD, with its similar bidirectional framework, faces the same problem. The untrustworthiness of the detector also increases the risk of side-channel attacks. Another issue is performance. Current SQKD protocols are insufficient in terms of key efficiency and transmission distance. As the scale of quantum communication networks expands and the number of users increases, the performance requirements for SQKD systems become increasingly demanding. Existing SQKD systems struggle to meet the needs of long-distance, high-speed communication. Summary of the Invention

[0005] The purpose of this application is to provide a semi-quantum key distribution method and system suitable for hybrid networking, which can meet the application needs of different scenarios and improve the key rate and security in semi-quantum communication.

[0006] To achieve the above objectives, this application provides the following solution:

[0007] Firstly, this application provides a semi-quantum key distribution method suitable for hybrid networking, including:

[0008] Determine the node status in the hybrid network; the node status is either trusted or untrusted.

[0009] If the node status is trusted, then the nodes in the hybrid network use a one-way coded semi-quantum key distribution protocol for key distribution.

[0010] If the node status is device untrusted, then the nodes in the hybrid network use a dual-field semi-quantum key distribution protocol for key distribution;

[0011] The nodes in the hybrid network include one quantum side and two classical sides; the one-way coding semi-quantum key distribution protocol distributes the key to the two classical sides in the quantum direction; the two-field semi-quantum key distribution protocol sends a coherent state or a vacuum state to the quantum side in the two classical directions, and the two classical sides obtain the key based on a valid event in which no interference occurs.

[0012] Secondly, this application provides a semi-quantum key distribution system suitable for hybrid networking, including: a first classical party, a second classical party, a quantum party, a first quantum channel, and a second quantum channel; the first classical party is connected to the quantum party through the first quantum channel, and the second classical party is connected to the quantum party through the second quantum channel;

[0013] When a node in a hybrid network is in a trusted device state, the quantum side is used to distribute keys to the two classical sides;

[0014] When a node in a hybrid network is in an untrusted state, the first classical party and the second classical party are used to send a weakly coherent state or a vacuum state to the quantum party; the quantum party is used to perform interferometric measurements on the received photons; the first classical party and the second classical party are also used to obtain a key based on a valid event in which no interference has occurred.

[0015] According to the specific embodiments provided in this application, this application has the following technical effects:

[0016] This application provides a semi-quantum key distribution method and system suitable for hybrid networking. It achieves switching between two communication protocols through non-standalone networking technology. Within the same system, it supports both unidirectional coding semi-quantum key distribution protocols and dual-field semi-quantum key distribution protocols, enabling hybrid networking from trusted nodes to untrusted nodes. Specifically, two classical parties code using a dual-field semi-quantum key distribution protocol, and each then codes with a quantum party using a unidirectional coding semi-quantum key distribution protocol. Users can apply for different semi-quantum key distribution services to meet the application needs of different scenarios, and this improves the key rate and security in semi-quantum communication. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a semi-quantum key distribution method suitable for hybrid networking, provided as an embodiment of this application;

[0019] Figure 2 This is a schematic diagram illustrating the key distribution process using a one-way coded semi-quantum key distribution protocol in one embodiment of this application;

[0020] Figure 3 This is a schematic diagram illustrating the key distribution process using a dual-field semi-quantum key distribution protocol in one embodiment of this application;

[0021] Figure 4 This is a schematic diagram of a semi-quantum key distribution system suitable for hybrid networking, provided as an embodiment of this application.

[0022] Figure reference numerals: Alice - first classical square, Bob - second classical square, Charlie - quantum square, 101 - first light source, 102 - first circulator, 103 - first detector, 104 - second detector, 105 - first beam splitter, 106 - first polarization rotator, 107 - second beam splitter, 108 - first phase modulator, 109 - second circulator, 110 - second light source, 111 - first polarization beam splitter, 112 - third detector, 113 - second polarization rotator, 114 - third beam splitter, 115 - second phase modulator, 116 - third circulator, 117 - third light source, 118 - second polarization beam splitter, 119 - fourth detector, 121 - first optical delay coil, 122 - second optical delay coil, 123 - first quantum channel, 124 - second quantum channel. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The purpose of this application is to address the issues of insufficient key rate and security in existing semi-quantum communication. Based on time reversal, a high-performance semi-quantum communication network is proposed, enabling switching between two communication protocols. Through a hybrid networking architecture from trusted nodes to untrusted nodes, dynamic switching between a unidirectional coded semi-quantum key distribution protocol and a dual-field semi-quantum key distribution protocol is achieved to meet the application needs of different scenarios. When the device is untrusted, the "send from both sides to the middle" mode can be switched; when the device is trusted, the "send from the middle to both sides" mode can be switched. The qubit utilization efficiency of the unidirectional coded semi-quantum key distribution protocol reaches 50%, which is twice that of the BB84 protocol (25%). Furthermore, this application requires almost no hardware changes, resulting in extremely low cost. It allows the unidirectional coded semi-quantum key distribution protocol to support the dual-field semi-quantum key distribution protocol, enabling the deployment of an untrusted node network using the dual-field semi-quantum key distribution protocol, thus solving the security problem.

[0025] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] In one exemplary embodiment, such as Figure 1 As shown, a semi-quantum key distribution method suitable for hybrid networking is provided, including the following steps 11 to 13.

[0027] Step 11: Determine the node status in the hybrid network. The node status is either trusted or untrusted.

[0028] In this application, the nodes in the hybrid network include one quantum side and two classical sides. A one-way coding semi-quantum key distribution protocol distributes keys to the two classical sides in the quantum direction. A two-field semi-quantum key distribution protocol sends a coherent state or a vacuum state to the quantum side in the two classical directions, and the two classical sides obtain the key based on a valid event where no interference occurs.

[0029] Step 12: If the node status is trusted, then the nodes in the hybrid network use a one-way coded semi-quantum key distribution protocol for key distribution.

[0030] Specifically, if the measurement equipment is reliable and the information transmission distance is relatively short, a one-way coded semi-quantum key distribution protocol is selected, i.e., switching to the "middle-to-two" mode to form a trusted node network. In this mode, the quantum party acts as a trusted node, simultaneously distributing keys to two classical parties, as follows: Figure 2As shown. Specifically, the quantum side prepares a weakly coherent state and sends it to the classical sides at both ends of the interferometer. When one side measures and receives the photon, the key is generated. If an eavesdropper performs measurements in the channel, it will affect the interference result, increase the error rate of the returned bits, and thus establish the relationship between the eavesdropper's information content and the error rate. In the one-way key generation semi-quantum key distribution protocol, the unidirectionally transmitted qubits are used for key generation, and the bidirectionally transmitted qubits are used to detect whether there is eavesdropping. This can effectively solve the Trojan horse attack problem that is common in bidirectional systems, and enable the quantum side to distribute keys to two classical sides simultaneously, with a qubit utilization efficiency of up to 50%.

[0031] In a specific application example, step 12 includes steps 21 to 23.

[0032] Step 21: A weakly coherent state is prepared using a quantum square. Each photon is then polarized and split into two pulses, which are sent to two classical squares respectively. The two classical squares randomly select to return a photon or measure a photon and publish the corresponding return or measurement operation. A code of 0 indicates the preparation of a horizontally polarized photon, and a code of 1 indicates the preparation of a vertically polarized photon.

[0033] Step 22: If both classical methods simultaneously choose to return photons, the polarization direction of the photons is randomly flipped upon return. The quantum method then performs interferometry measurements on the photons returned by the classical methods to obtain the interferometry results, which are used to detect eavesdropping.

[0034] The measurement results for each round of communication include interferometric measurements of photons with the same polarization direction in two classical directions, and non-interferometric measurements of photons with different polarization directions in two classical directions. The interferometric measurements include those obtained by flipping photons in both classical directions, and those obtained by not flipping photons in either classical direction. Non-interferometric measurements obtained by flipping photons in one classical direction while not flipping photons in the other are discarded.

[0035] Step 23: If any classical method chooses to measure a photon, the photon is obtained through the measurement by the classical method, the polarization state of the photon is determined, and the key sent by the quantum method is obtained based on the polarization state of the photon.

[0036] Specifically, the quantum side determines the user and communication key for each round of communication based on the photon situation measured by the classical side, including: if the first classical side measures and obtains a photon, then the quantum side obtains the key sent by the quantum side based on the polarization state of the photon; if the second classical side measures and obtains a photon, then the quantum side obtains the key sent by the quantum side based on the polarization state of the photon.

[0037] In one embodiment, the quantum key distribution party simultaneously distributes keys to both the first and second classical key distribution parties. If the first classical key distribution party chooses to return a photon, and the second classical key distribution party chooses to measure a photon, and the photon happens to be directed to the second classical key distribution party, then the second classical key distribution party obtains the photon and determines its polarization state based on the measurement result. The qubit utilization efficiency in this case is 12.5%. If the second classical key distribution party chooses to return a photon, and the first classical key distribution party chooses to measure a photon, and the photon happens to be directed to the first classical key distribution party, then the first classical key distribution party obtains the photon and determines its polarization state based on the measurement result. The qubit utilization efficiency in this case is 12.5%. If both the first and second classical key distribution parties simultaneously choose to measure a photon, they both obtain the photon and determine its polarization state based on the measurement result. The qubit utilization efficiency in this case is 25%, and the qubit utilization efficiency of the one-way coding semi-quantum key distribution protocol can reach 50%.

[0038] Existing semi-quantum key distribution protocols rely on bidirectional quantum channels. A first classical party sends light pulses to a second classical party via a quantum channel, and the second classical party encodes the pulses and returns them to the first classical party for measurement, thus transmitting information. However, practical bidirectional systems have more security vulnerabilities. Compared to unidirectional communication, Eve can exploit the photon return process to launch more side-channel attacks in bidirectional systems; such attacks are known as Trojan horse attacks. This application addresses the security vulnerabilities in bidirectional systems by using unidirectionally transmitted bits for encoding and the returned bits for eavesdropping detection.

[0039] Step 13: If the node status is device untrusted, then the nodes in the hybrid network use a dual-field semi-quantum key distribution protocol for key distribution.

[0040] Specifically, if the measurement equipment is untrusted and the information transmission distance is long, a dual-field semi-quantum key distribution protocol is selected, i.e., switching to a "send from both sides to the middle" mode, forming a network of untrusted nodes. The process is as follows: Figure 3 As shown. In this mode, through time reversal, two classical parties act as two transmitters, and a quantum party acts as a receiver. The two classical parties share the same secure key based on the Bell state measurement results published by the quantum party. Throughout the process, the quantum party's measurement results do not affect the security of communication, thus achieving untrusted node networking. Specifically, the two classical parties randomly prepare coherent states |α> and vacuum states |0> with fixed phases, encode each photon by whether it is transmitted or not, and send it to the quantum party. The quantum party performs interferometric measurements on the received pulses. For non-interferometric measurement results, the key value is determined solely by whether a photon is received or not. The dual-field semi-quantum key distribution protocol does not require phase randomization of the optical pulses.

[0041] In a specific application example, step 13 includes steps 31 to 34.

[0042] Step 31: Weakly coherent states and vacuum states are randomly prepared using two classical methods, and each photon is encoded and sent to the quantum method. The two classical methods choose to send either a weakly coherent state or a vacuum state to the quantum method. Encoding 1 indicates sending a weakly coherent state with a fixed phase. Encoding 0 indicates sending a vacuum state.

[0043] Step 32: Perform interferometric measurement on each received photon using the quantum square.

[0044] If both classical sides simultaneously choose to send weakly coherent states, single-photon interference occurs in the quantum side, meaning that the first detector in the quantum side responds to the interference, while the second detector does not.

[0045] If one classical side chooses to send a weakly coherent state and the other chooses to send a vacuum state, no single-photon interference occurs on the quantum side; that is, the first and second detectors respond probabilistically, and the second detector acts as a coded mode detector. If both classical sides simultaneously choose to send a vacuum state, the quantum side will not detect any photons.

[0046] Step 33: If the measurement result is that no interference occurred, the two classical methods identify the valid events in which no interference occurred and obtain the key corresponding to each photon.

[0047] Step 34: If the measurement result indicates interference, the two classical methods detect eavesdropping based on the interference response results.

[0048] Single-photon interference results in the first detector of the quantum side responding to interference while the second detector does not. The interference result is used to detect eavesdropping. Based on the response of the second detector, it is determined that the codes of the two classical parties in this round of communication are opposite. The absence of interference between the two signal lights leads to probabilistic responses from the first and second detectors. The second detector is a coded pattern detector. Based on the responses from the second detector of the coded pattern, the two classical parties identify valid events where no interference occurred and obtain the original key corresponding to each photon.

[0049] In the dual-field semi-quantum key distribution protocol, the key value is determined solely by whether a photon is received. Only a single detector response is required. When the coding mode detector responds, the codes of the two classical sides are inversely correlated. However, the quantum side cannot know whether the codes of the two classical sides are 0 or 1. Therefore, the security of the dual-field semi-quantum key distribution protocol is independent of the measurement device. Each effective probe used by the quantum side for code generation consumes only one photon, which only traverses a single-sided channel. This allows it to break the linear limit of code generation rate without quantum repeaters, making it more suitable for long-distance transmission.

[0050] In this application, the key is distributed only when there is no interference between the signal beams sent by the two classical parties during the key distribution process using a dual-field semi-quantum key distribution protocol. Based on the valid events of no interference published by the quantum party, the two classical parties retain the corresponding signal codes as the key. Furthermore, the valid events are only single-photon response events, resulting in a relatively high key generation rate and key rate. It also has the security advantage of being independent of measurement devices and enables the transition from trusted node networking to untrusted node networking.

[0051] In summary, this application utilizes time reversal to switch between two modes: "transmission from the middle to both ends" and "transmission from both ends to the middle," enabling the implementation of different communication protocols within the same system. Depending on the application scenario and the trustworthiness of the devices, non-standalone networking technology is used to achieve switching between the two communication protocols. Within the same system, both unidirectional semi-quantum key distribution protocols and dual-field semi-quantum key distribution protocols can be supported, achieving hybrid networking from trusted nodes to untrusted nodes.

[0052] Based on the same inventive concept, this application also provides a system for implementing the methods described above. The solution provided by this system is similar to the solution described in the methods above; therefore, specific limitations in one or more system embodiments provided below can be found in the limitations of the methods described above, and will not be repeated here.

[0053] In one exemplary embodiment, such as Figure 4 As shown, a semi-quantum key distribution system suitable for hybrid networking is provided, comprising: a first classical party Alice, a second classical party Bob, a quantum party Charlie, a first quantum channel 123, and a second quantum channel 124. The first classical party Alice is connected to the quantum party Charlie through the first quantum channel 123, and the second classical party Bob is connected to the quantum party Charlie through the second quantum channel 124.

[0054] When a node in a hybrid network is in a trusted device state, the quantum side Charlie is used to distribute keys to the two classical sides.

[0055] When a node in a hybrid network is in an untrusted state, the first classical party Alice and the second classical party Bob send a weakly coherent state or a vacuum state to the quantum party Charlie. The quantum party Charlie then performs interferometric measurements on the received photons. Alice and Bob also obtain a key based on valid events where no interference occurs.

[0056] The semi-quantum key distribution system provided in this application can implement two communication modes: a one-way coding semi-quantum key distribution protocol and a dual-field semi-quantum key distribution protocol. When these two communication modes coexist, one or both can be selected for communication according to application requirements, or they can communicate simultaneously to achieve a hybrid network of trusted and untrusted nodes. When different communication modes are selected, the individual devices of the two classical sides differ in function.

[0057] The quantum node Charlie is connected to the first classical node Alice and the second classical node Bob using a Michelson interferometer. On one hand, Alice and Bob use a one-way coding semi-quantum key distribution protocol to generate codes, achieving a trusted node network. On the other hand, Alice and Bob each multiply codes with the quantum node Charlie using a dual-field semi-quantum key distribution protocol, achieving an untrusted node network. This application simultaneously supports both the one-way coding semi-quantum key distribution protocol and the dual-field semi-quantum key distribution protocol, realizing a hybrid network from trusted nodes to untrusted nodes, which greatly improves the overall practicality and security of the semi-quantum communication network.

[0058] In a specific application example, the quantum square Charlie includes: a first light source 101, a first circulator 102, a first beam splitter 105, a first detector 103, and a second detector 104.

[0059] The first port of the first circulator 102 is connected to the first detector 103, the second port of the first circulator 102 is connected to the first port of the first beam splitter 105, and the third port of the first circulator 102 is connected to the emission port of the first light source 101.

[0060] The second port of the first beam splitter 105 is connected to the second detector 104, the third port of the first beam splitter 105 is connected to the input port of the first quantum channel 123, and the fourth port of the first beam splitter 105 is connected to the input port of the second quantum channel 124.

[0061] In a specific application example, the first classical Alice includes: a first polarization rotator 106, a second beam splitter 107, a first phase modulator 108, a second circulator 109, a second light source 110, a first polarization beam splitter 111, and a third detector 112.

[0062] One end of the first polarization rotator 106 is connected to the output port of the first quantum channel 123.

[0063] The first port of the second beam splitter 107 is connected to the other end of the first polarization rotator 106, the second port of the second beam splitter 107 is connected to the first port of the second circulator 109, the third port of the second beam splitter 107 is connected to the first port of the first phase modulator 108, and the fourth port of the second beam splitter 107 is connected to the second port of the first phase modulator 108.

[0064] The second port of the second circulator 109 is connected to the second light source 110, and the third port of the second circulator 109 is connected to the first port of the first polarization beamsplitter 111 (specifically, the first port of the combination of the first polarization beamsplitter 111 and the first optical delay coil 121). The second port of the first polarization beamsplitter 111 is connected to the third detector 112, and the third port of the first polarization beamsplitter 111 is connected to the third detector 112 through the first optical delay coil 121.

[0065] When a node in the hybrid network is in a trusted device state, a first optical switch is formed by the Sagnac ring interferometer based on the second beam splitter 107 and the first phase modulator 108, enabling pulse return or measurement operations. When a node in the hybrid network is in an untrusted device state, a first intensity modulator is formed by the Sagnac ring interferometer based on the second beam splitter 107 and the first phase modulator 108, enabling pulse transmission and non-pulse transmission operations.

[0066] In a specific application example, the second classical square Bob includes: a second polarization rotator 113, a third beam splitter 114, a second phase modulator 115, a third circulator 116, a third light source 117, a second polarization beam splitter 118, and a fourth detector 119.

[0067] One end of the second polarization rotator 113 is connected to the output port of the second quantum channel 124.

[0068] The first port of the third beam splitter 114 is connected to the other end of the second polarization rotator 113, the second port of the third beam splitter 114 is connected to the first port of the third circulator 116, the third port of the third beam splitter 114 is connected to the first port of the second phase modulator 115, and the fourth port of the third beam splitter 114 is connected to the second port of the second phase modulator 115.

[0069] The second port of the third circulator 116 is connected to the third light source 117, and the third port of the third circulator 116 is connected to the first port of the second polarization beamsplitter 118 (specifically, the first port of the combination of the second polarization beamsplitter 118 and the second optical delay coil 122). The second port of the second polarization beamsplitter 118 is connected to the fourth detector 119. The third port of the second polarization beamsplitter 118 is connected to the fourth detector 119 through the second optical delay coil 122.

[0070] When a node in the hybrid network is in a trusted device state, a second optical switch is formed by the Sagnac ring interferometer based on the third beam splitter 114 and the second phase modulator 115, enabling pulse return or measurement operations. When a node in the hybrid network is in an untrusted device state, a second intensity modulator is formed by the Sagnac ring interferometer based on the third beam splitter 114 and the second phase modulator 115, enabling pulse transmission and non-pulse transmission operations.

[0071] In this application, the intensity modulator is used to achieve high-speed intensity modulation, generating weakly coherent states and vacuum states for coding. The optical switches (including a first optical switch and a second optical switch) and the intensity modulators (including a first intensity modulator and a second intensity modulator) have the same optical path structure but different functions. When switching to a unidirectional coding semi-quantum key distribution protocol, the optical switch function can be implemented. When switching to a dual-field semi-quantum key distribution protocol, the intensity modulator function can be implemented, achieving high integration.

[0072] The transmittance-to-reflection ratios of the first beam splitter 105, the second beam splitter 107, and the third beam splitter 114 are all 50:50.

[0073] The working process of the semi-quantum key distribution system for hybrid networking provided in this application is described below.

[0074] 1) For trusted node networking, that is, the node status in the hybrid network is trusted device.

[0075] In the trusted quantum square Charlie, a first light source 101 is used to randomly prepare weakly coherent states polarized in either the horizontal or vertical direction. The prepared weakly coherent states polarized in the horizontal direction are encoded as 0, and the prepared weakly coherent states polarized in the vertical direction are encoded as 1. The prepared signal light is sent to the third port of the first circulator 102. The signal light exits from the second port of the first circulator 102 and then enters the first port of the first beamsplitter 105, where it is split into two sub-pulses, exiting from the third and fourth ports of the first beamsplitter 105, respectively. The two sub-pulses enter the first classical square Alice and the second classical square Bob, respectively. The first classical square Alice and the second classical square Bob use a first optical switch and a second optical switch, respectively, to randomly select between returning or measuring the incoming pulses.

[0076] In this embodiment, the first optical switch can be controlled to open and close by adjusting the first phase modulator 108. The sub-pulse entering the first classical Alice is incident from the first port of the second beamsplitter 107, and is then split into two sub-pulses, which exit from the third and fourth ports respectively. If the phase modulation of the first phase modulator 108 is 0, the two sub-pulses interfere with each other in the second beamsplitter 107 and ultimately exit from the first port of the second beamsplitter 107, corresponding to the first optical switch being closed, i.e., the first classical Alice returning photons. If the phase modulation of the first phase modulator 108 is π, the two sub-pulses interfere with each other in the second beamsplitter 107 and change the pulse exit direction, ultimately exiting from the second port of the second beamsplitter 107, corresponding to the first optical switch being open, i.e., the first classical Alice measuring photons. The second optical switch follows the same working principle as the first optical switch.

[0077] If Alice (the first classical party) and Bob (the second classical party) close the optical switches, the corresponding return pulse operation is selected. Simultaneously closing both optical switches will cause the two sub-pulses to return to the trusted quantum party Charlie via their original paths. The two returning pulses are randomly flipped by the first polarization rotator 106 and the second polarization rotator 113, respectively. The quantum party Charlie then measures the returned photons. Based on the interference results, the quantum party Charlie detects eavesdropping.

[0078] The light is again incident from the third and fourth ports of the first beam splitter 105 and interferes. Finally, it exits from the first port of the first beam splitter and reaches the second port of the first circulator 102, exiting from its first port and causing the first detector 103 to respond. The interference result is used to detect whether eavesdropping is present. The principle of the second classical method Bob and the first classical method Alice in selecting the measurement pulse operation is the same.

[0079] If Alice, the first classical method, opens the first optical switch, correspondingly selecting the measurement pulse operation, the first optical switch sends a sub-pulse to the first port of the first polarization beamsplitter 111. The first polarization beamsplitter 111 then sends pulses of different polarization states to the third detector 112, causing it to respond. Specifically, if the sub-pulse is horizontally polarized light, it exits from its second port; if the sub-pulse is vertically polarized light, it exits from its third port and passes through the first optical delay coil 121. The purpose is to ensure that pulses of different polarization states arrive at the third detector 112 at different times, achieving time distinguishability and thus enabling the differentiation of pulses of different polarization states. Bob, the second classical method, operates on the same principle as Alice, selecting the measurement pulse operation.

[0080] In the above scenarios, if Alice (the first classical party) chooses to return the photon, and Bob (the second classical party) chooses to measure and obtain the photon, and determines the polarization state of the photon based on the measurement result, the qubit utilization efficiency is 12.5%. If Bob (the second classical party) chooses to return the photon, and Alice (the first classical party) chooses to measure and obtain the photon, and determines the polarization state of the photon based on the measurement result, the qubit utilization efficiency is 12.5%. If Alice (the first classical party) and Bob (the second classical party) simultaneously choose to measure the photon, and one of them obtains the photon and determines the polarization state of the photon based on the measurement result, the qubit utilization efficiency is 25%. The qubit utilization efficiency of this protocol reaches 50%.

[0081] 2) For untrusted node networking, that is, the node status in the hybrid networking is untrusted device.

[0082] Through time reversal, Alice (the first classical party) and Bob (the second classical party) act as transmitters to send qubits. Alice or Bob transmits a weakly coherent state encoded as 1, and a vacuum state encoded as 0. Alice prepares the weakly coherent state using a second light source 110; Bob prepares the weakly coherent state using a third light source 117. The two signal beams are incident from the second port of the second circulator 109 and the second port of the third circulator 116, respectively, and exit from the first port, entering the first and second intensity modulators, respectively. Alice and Bob use the first and second intensity modulators, respectively, to control whether to transmit or not.

[0083] In this embodiment: the first intensity modulator can modulate the intensity of its signal light by adjusting the first phase modulator 108. The weakly coherent state prepared by the first classical Alice is incident from the second port of the second beamsplitter 107, and then split into two sub-pulses by the second beamsplitter 107, exiting from its third and fourth ports respectively. If the phase is modulated to 0 by the first phase modulator 108, the two sub-pulses interfere with each other in the second beamsplitter 107, and finally exit from the second port of the second beamsplitter 107, corresponding to the vacuum state transmitted by the first classical Alice; if the phase is modulated to π by the first phase modulator 108, the two sub-pulses interfere with each other in the second beamsplitter 107 and change the pulse exit direction, and finally exit from the first port of the second beamsplitter 107, corresponding to the weakly coherent state transmitted by the first classical Alice. The second intensity modulator follows the same working principle as the first intensity modulator.

[0084] If Alice (first classical) and Bob (second classical) simultaneously choose to send a weakly coherent state, the two signal beams will interfere after passing through and entering the third and fourth ports of the first beam splitter. They will then exit from the first port of the first beam splitter and reach the second port of the first circulator 102, and finally exit from its first port, causing the first detector 103 to respond. The interference result detected is used to detect whether eavesdropping is present.

[0085] If Alice, the first classical party, chooses to send a weakly coherent state, and Bob, the second classical party, chooses to send a vacuum state; or Alice, the first classical party, sends a vacuum state, and Bob, the second classical party, chooses to send a weakly coherent state; then the two signal beams sent by Alice and Bob are incident from the third and fourth ports of the first beam splitter, respectively, but do not interfere. Instead, they exit from the first or second port of the first beam splitter 105, respectively, causing the first detector 103 or the second detector 104 to respond probabilistically.

[0086] If the second detector 104 responds, it indicates that Alice, the first classical party, and Bob, the second classical party, have chosen a weakly coherent state and a vacuum state, respectively. The key can only be distributed when there is no interference between the signal lights sent by Alice and Bob. According to the valid event of no interference published by Charlie, the first classical party Alice and Bob will encode and retain the corresponding signals as the key. One of the two classical parties will flip its own bits and share the key with the other party.

[0087] This application reverses the execution process of a semi-quantum key distribution protocol in time. Two classical parties, acting as senders, prepare signal light according to whether photons are detected (either by transmitting or not transmitting), and then send it to the quantum party, Charlie. The quantum party, Charlie, performs Bell state measurements on the photons sent by the two classical parties, identifying valid detection events without interference. Only a single detector response is required, and the two classical parties encode an anti-correlation relationship. However, the quantum party, Charlie, cannot know whether the classical parties' codes are 0 or 1, thus enabling a dual-field semi-quantum key distribution protocol. This process allows for the implementation of different protocol schemes within the same system, namely, switching between the "middle-to-two" communication protocol of unidirectional coding semi-quantum key distribution and the "two-to-middle" communication protocol of dual-field interference semi-quantum key distribution.

[0088] In summary, compared with the prior art, this application has at least the following beneficial effects:

[0089] (1) Enhanced security: The one-way coding semi-quantum key distribution protocol solves the security risks of bidirectional systems by reducing assumptions about the quantum state at the source end and by detecting eavesdropping through the bit returned after encoding the unidirectional transmitted bits; the dual-field semi-quantum key distribution protocol utilizes the principle of single-photon interference to create entangled states between the communicating parties, thereby completing the key generation. This design inherits the basic architecture of measurement-device-independent protocols and has extremely high security.

[0090] (2) Improved performance: In the one-way coding semi-quantum key distribution protocol, the quantum party Charlie sends the key to two classical parties at the same time, and the quantum bit utilization efficiency reaches 50%, which is twice that of the BB84 protocol; the dual-field semi-quantum key distribution protocol can extend the distance of semi-quantum key distribution to a certain extent, which helps to realize the interconnection of networks between cities.

[0091] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0092] In this application, all actions to acquire signals, information, or data are carried out in compliance with the relevant data protection laws and policies of the country where the location is situated, and with the authorization granted by the owner of the relevant device.

[0093] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0094] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A semi-quantum key distribution method suitable for hybrid networking, characterized in that, The method includes: Determine the node status in the hybrid network; the node status is either trusted or untrusted. If the node status is trusted, then the nodes in the hybrid network use a one-way coded semi-quantum key distribution protocol for key distribution. If the node status is device untrusted, then the nodes in the hybrid network use a dual-field semi-quantum key distribution protocol for key distribution; The nodes in the hybrid network include one quantum side and two classical sides; the one-way coding semi-quantum key distribution protocol distributes the key to the two classical sides in the quantum direction; the dual-field semi-quantum key distribution protocol sends a coherent state or a vacuum state to the quantum side in the two classical directions, and the two classical sides obtain the key based on a valid event in which no interference occurs. The nodes in the hybrid network use a one-way coded semi-quantum key distribution protocol for key distribution. Specifically, this includes: preparing weakly coherent states using a quantum square, and then polarizing each photon and splitting it into two pulses, which are sent to two classical squares respectively; the two classical squares randomly choose to return a photon or measure a photon; if both classical squares simultaneously choose to return a photon, the polarization direction of the returned photon is randomly flipped; the quantum square performs interferometry on the photon returned by the classical square to obtain the interferometry result for detecting eavesdropping; if either classical square chooses to measure a photon, the photon is measured by the classical square, its polarization state is determined, and the key sent by the quantum square is obtained based on the polarization state of the photon. The nodes in the hybrid network use a dual-field semi-quantum key distribution protocol for key distribution, specifically including: randomly preparing weakly coherent states and vacuum states by two classical parties, encoding each photon, and sending it to the quantum party; the quantum party performing an interference measurement on each received photon; if the measurement result is no interference, the two classical parties identify the valid event of no interference and obtain the key corresponding to each photon; if the measurement result is interference, the two classical parties detect eavesdropping based on the interference response result. When a node in the hybrid network is in a trusted device state, a Sagnac ring interferometer based on the first classical method and the first phase modulator forms a first optical switch to realize the return or measurement operation of the pulse; when a node in the hybrid network is in a trusted device state, a Sagnac ring interferometer based on the first classical method and the first phase modulator forms a first intensity modulator to realize the operation of sending pulses and not sending pulses. When a node in the hybrid network is in a trusted device state, a Sagnac ring interferometer based on the second classical method and the second phase modulator constitutes a second optical switch to realize the return or measurement operation of the pulse; when a node in the hybrid network is in a trusted device state, a Sagnac ring interferometer based on the second classical method and the second phase modulator constitutes a second intensity modulator to realize the operation of sending pulses and not sending pulses.

2. The semi-quantum key distribution method suitable for hybrid networking according to claim 1, wherein, If both classical parties simultaneously choose to send a weakly coherent state, the measurement result is interference; if one classical party chooses to send a weakly coherent state and the other classical party chooses to send a vacuum state, the measurement result is no interference; if both classical parties simultaneously choose to send a vacuum state, the quantum party cannot detect the photon.

3. A semi-quantum key distribution system suitable for hybrid networking, characterized by, The system is applied to the semi-quantum key distribution method for hybrid networking as described in any one of claims 1-2, the system comprising: a first classical party, a second classical party, a quantum party, a first quantum channel, and a second quantum channel; the first classical party is connected to the quantum party through the first quantum channel, and the second classical party is connected to the quantum party through the second quantum channel; When a node in a hybrid network is in a trusted device state, the quantum side is used to distribute keys to the two classical sides; When a node in a hybrid network is in an untrusted state, the first classical party and the second classical party are used to send a weakly coherent state or a vacuum state to the quantum party; the quantum party is used to perform interferometric measurements on the received photons; the first classical party and the second classical party are also used to obtain a key based on a valid event in which no interference has occurred.

4. The semi-quantum key distribution system suitable for hybrid networking according to claim 3, wherein, The quantum square includes: a first light source, a first circulator, a first beam splitter, a first detector, and a second detector; The first port of the first circulator is connected to the first detector, the second port of the first circulator is connected to the first port of the first beam splitter, and the third port of the first circulator is connected to the emission port of the first light source. The second port of the first beam splitter is connected to the second detector, the third port of the first beam splitter is connected to the input port of the first quantum channel, and the fourth port of the first beam splitter is connected to the input port of the second quantum channel.

5. The semi-quantum key distribution system suitable for hybrid networking according to claim 3, characterized in that, The first classical method includes: a first polarization rotator, a second beam splitter, a first phase modulator, a second circulator, a second light source, a first polarization beam splitter, and a third detector; One end of the first polarization rotator is connected to the output port of the first quantum channel; The first port of the second beam splitter is connected to the other end of the first polarization rotator, the second port of the second beam splitter is connected to the first port of the second circulator, the third port of the second beam splitter is connected to the first port of the first phase modulator, and the fourth port of the second beam splitter is connected to the second port of the first phase modulator. The second port of the second circulator is connected to the second light source, and the third port of the second circulator is connected to the first port of the first polarization beamsplitter; the second port of the first polarization beamsplitter is connected to the third detector, and the third port of the first polarization beamsplitter is connected to the third detector through a first optical delay coil.

6. The semi-quantum key distribution system suitable for hybrid networking according to claim 3, characterized in that, The second classical method includes: a second polarization rotator, a third beam splitter, a second phase modulator, a third circulator, a third light source, a second polarization beam splitter, and a fourth detector; One end of the second polarization rotator is connected to the output port of the second quantum channel; The first port of the third beam splitter is connected to the other end of the second polarization rotator, the second port of the third beam splitter is connected to the first port of the third circulator, the third port of the third beam splitter is connected to the first port of the second phase modulator, and the fourth port of the third beam splitter is connected to the second port of the second phase modulator. The second port of the third circulator is connected to the third light source, and the third port of the third circulator is connected to the first port of the second polarization beam splitter; the second port of the second polarization beam splitter is connected to the fourth detector; the third port of the second polarization beam splitter is connected to the fourth detector through a second optical delay coil.

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