Semi-quantum key distribution method and system suitable for hybrid networking

Abstract

The invention discloses a semi-quantum key distribution method and system suitable for hybrid networking, and relates to the field of key distribution, and the method comprises the steps: determining a node state in the hybrid networking; the node state is equipment credible or equipment uncredible; if the node state is that the equipment is credible, the nodes in the hybrid network adopt a one-way coding semi-quantum key distribution protocol to carry out key distribution; if the node state is that the equipment is not credible, the nodes in the hybrid network adopt a double-field semi-quantum key distribution protocol to carry out key distribution; nodes in the hybrid network comprise a quantum party and two classic parties; the one-way coding semi-quantum key distribution protocol distributes keys for two classic parties in the quantum direction; according to the double-field semi-quantum key distribution protocol, coherent states or vacuum states are sent to quantum parties in two classic directions, and the two classic parties obtain keys according to effective events without interference. According to the invention, the application requirements of different scenes can be met, and the key rate and security in semi-quantum communication are improved.

Description

TECHNICAL FIELD

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

[0002] Quantum Key Distribution (QKD) technology mainly uses quantum mechanics principles for information transmission and encryption, and is considered as the key to future information security transmission. However, the application prospect of QKD protocol is still limited by hardware foundation, especially as the number of users increases, the complexity of network structure and the difficulty of user shared reference system parameters increase dramatically.

[0003] Semi-Quantum Key Distribution (SQKD) is a communication protocol in which one of the two communicating parties is a quantum party and the other is a classical party (can only use a set of basis vectors to prepare or measure quantum states), which can still achieve secure key exchange of quantum cryptography technology. Its core advantage compared to QKD is that in semi-quantum communication, even if the classical party cannot completely prepare or measure quantum states, it can still achieve unconditional secure key exchange in the information theory sense through a specific protocol; the classical party does not need complex quantum devices, reducing the cost and technical threshold of entering the network, making quantum communication more popular.

[0004] Although SQKD technology has made some progress, there are still some key technical problems that restrict its practical application and development. On the one hand, the security problem, due to the existence of device flaws, modulation errors, environmental interference and other factors, there will be a problem of eavesdropping. For example, in a two-way QKD system, Trojan horse attack is a serious security risk, and SQKD also faces this problem due to its similar two-way framework, and the untrustworthiness of the detector also increases the risk of side-channel attacks. On the other hand, the performance problem, the current SQKD protocol has deficiencies in key efficiency and transmission distance. With the expansion of quantum communication network scale and the increase of user number, the performance requirement of SQKD system is also getting higher and higher. The existing SQKD system is difficult to meet the demand of long-distance and high-speed communication. SUMMARY

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

[0006] To achieve the above purpose, the present application provides the following solutions: In a first aspect, the present application provides a semi-quantum key distribution method suitable for hybrid networking, comprising: determining a node state in the hybrid networking; the node state is device trusted or device untrusted; if the node state is device trusted, the nodes in the hybrid networking adopt a one-way code forming semi-quantum key distribution protocol for key distribution; if the node state is device untrusted, the nodes in the hybrid networking adopt a two-field semi-quantum key distribution protocol for key distribution; the nodes in the hybrid networking include one quantum party and two classical parties; the one-way code forming semi-quantum key distribution protocol distributes keys for the quantum party and the two classical parties; the two-field semi-quantum key distribution protocol sends coherent states or vacuum states for the quantum party from the two classical parties, and the two classical parties obtain keys according to valid events without interference.

[0007] In a second aspect, the application provides a semi-quantum key distribution system suitable for hybrid networking, 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 with the quantum party through the first quantum channel, and the second classical party is connected with the quantum party through the second quantum channel. when the node state in the hybrid networking is device trusted, the quantum party is configured to distribute keys for the two classical parties; when the node state in the hybrid networking is device untrusted, the first classical party and the second classical party are configured to send weak coherent states or vacuum states for the quantum party; the quantum party is configured to perform interference measurement on the received photons; and the first classical party and the second classical party are further configured to obtain keys according to valid events without interference.

[0008] According to the specific embodiments provided by the application, the application has the following technical effects: The application provides a semi-quantum key distribution method and system suitable for hybrid networking, which realizes mutual switching of two communication protocols through non-independent networking technology, supports both one-way code forming semi-quantum key distribution protocol and two-field semi-quantum key distribution protocol in the same system, and realizes hybrid networking from trusted nodes to untrusted nodes. Among them, the two classical parties form codes in the two-field semi-quantum key distribution protocol, and they respectively form codes with the quantum party in the one-way code forming semi-quantum key distribution protocol, so that users can apply for different semi-quantum key distribution services to meet the application requirements of different scenes, and the key rate and security in semi-quantum communication are improved. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below only illustrate some of the embodiments of the present application, and for those skilled in the art, other drawings can be obtained based on these drawings without creative labor.

[0010] Figure 1 A flowchart of a semi-quantum key distribution method suitable for hybrid networking provided by an embodiment of the present application; Figure 2 A process diagram of key distribution using a one-way code forming semi-quantum key distribution protocol in an embodiment of the present application; Figure 3 A process diagram of key distribution using a two-field semi-quantum key distribution protocol in an embodiment of the present application; Figure 4 A structure diagram of a semi-quantum key distribution system suitable for hybrid networking provided by an embodiment of the present application.

[0011] Reference signs: Alice-first classical party, Bob-second classical party, Charlie-quantum party, 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 DESCRIPTION

[0012] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0013] The purpose of the present application is to solve the problems of insufficient key rate and security in existing semi-quantum communication. A high-performance semi-quantum communication network is proposed based on time reversal, which can realize the switching of two communication protocols. Through the mixed networking architecture from trusted nodes to untrusted nodes, the dynamic switching of the one-way code semi-quantum key distribution protocol and the two-field semi-quantum key distribution protocol is realized to meet the application requirements of different scenarios. When the device is untrusted, the mode of "sending from both sides to the middle" can be switched. When the device is trusted, the mode of "sending from the middle to both sides" can be switched. The quantum bit utilization efficiency of the one-way code semi-quantum key distribution protocol is as high as 50%, which is twice the quantum bit utilization efficiency (25%) of the BB84 protocol. In addition, the present application almost does not need hardware changes and has very low cost. The one-way code semi-quantum key distribution protocol is used to support the two-field semi-quantum key distribution protocol, and the untrusted node network is deployed using the two-field semi-quantum key distribution protocol, which solves the security problem.

[0014] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below in combination with the drawings and specific embodiments.

[0015] In an exemplary embodiment, as shown in Figure 1 A semi-quantum key distribution method suitable for mixed networking is provided, which includes the following steps 11 to 13.

[0016] Step 11, determining the node state in the mixed networking. The node state is that the device is trusted or untrusted.

[0017] In the present application, the nodes in the mixed networking include one quantum side and two classical sides. The one-way code semi-quantum key distribution protocol distributes keys to the two classical sides from the quantum side. The two-field semi-quantum key distribution protocol sends coherent states or vacuum states to the quantum side from the two classical sides, and the two classical sides obtain keys according to effective events without interference.

[0018] Step 12, if the node state is that the device is trusted, the nodes in the mixed networking use the one-way code semi-quantum key distribution protocol for key distribution.

[0019] Specifically, if the measurement device is trusted and the information transmission distance is short, the one-way code semi-quantum key distribution protocol is selected, i.e., the "middle to both sides" mode is switched, forming a trusted node networking. In this mode, the quantum side acts as a trusted node and distributes keys to the two classical sides at the same time. The process is as shown in Figure 2Specifically, the quantum party prepares weak coherent states and sends the classical parties at both ends of the interferometer. When one of the parties measures and obtains a photon, the code is formed. If the eavesdropper measures in the channel, it will affect the interference result and increase the error rate of the returned bits, thereby establishing the relationship between the amount of information of the eavesdropper and the error rate. In the one-way coding semi-quantum key distribution protocol, the quantum bits transmitted in one direction are used for coding, and the quantum bits transmitted in both directions are used for detecting whether there is eavesdropping. The Trojan horse attack problem commonly existing in the two-way system can be effectively solved, and the quantum party can simultaneously distribute keys to two classical parties. The utilization efficiency of quantum bits is as high as 50%.

[0020] In one specific application example, step 12 includes steps 21 to 23.

[0021] Step 21, the quantum party prepares weak coherent states, and each photon is polarized and encoded and then divided into two pulses and sent to two classical parties. The two classical parties randomly select returned photons or measured photons, and announce the corresponding returned or measured operations. Among them, encoding 0 means preparing horizontally polarized photons. Encoding 1 means preparing vertically polarized photons.

[0022] Step 22, if the two classical parties simultaneously select returned photons, the polarization direction of the photon is randomly flipped when returned. The quantum party interferes and measures the returned photons of the classical party to obtain interference measurement results to detect eavesdropping.

[0023] The measurement results of each round of communication include the interference measurement results of the photons with the same polarization direction of the two classical parties, and the non-interference measurement results of the photons with different polarization directions of the two classical parties. The interference measurement results include the interference measurement results obtained after the two classical parties flip the photons, and the interference measurement results obtained after the two classical parties do not flip the photons. The non-interference measurement results obtained after one classical party flips the photon and the other classical party does not flip the photon are discarded.

[0024] Step 23, if any of the classical parties selects a measured photon, the photon is obtained by measuring the classical party, the polarization state of the photon is determined, and the key sent by the quantum party is obtained according to the polarization state of the photon.

[0025] Specifically, the quantum party determines the user of each round of communication and the key of the communication according to the photon obtained by the classical party measurement, including: if the first classical party measures and obtains a photon, the key sent by the quantum party is obtained according to the polarization state of the photon; if the second classical party measures and obtains a photon, the key sent by the quantum party is obtained according to the polarization state of the photon.

[0026] In an embodiment, the quantum party distributes the key to the first classical party and the second classical party at the same time. If the first classical party chooses to return the photon, the second classical party chooses to measure the photon, and the photon happens to go to the second classical party, the second classical party obtains the photon and determines the polarization state of the photon according to the measurement result. In this case, the quantum bit utilization efficiency is 12.5%. If the second classical party chooses to return the photon, the first classical party chooses to measure the photon, and the photon happens to go to the first classical party, the first classical party obtains the photon and determines the polarization state of the photon according to the measurement result. In this case, the quantum bit utilization efficiency is 12.5%. If the first classical party and the second classical party both choose to measure the photon at the same time, they both obtain the photon and determine the polarization state of the photon according to the measurement result. In this case, the quantum bit utilization efficiency is 25%, and the quantum bit utilization efficiency of the unidirectional coding semi-quantum key distribution protocol can reach 50%.

[0027] The existing semi-quantum key distribution protocol relies on a bidirectional quantum channel, i.e., the first classical party sends a light pulse to the second classical party through the quantum channel, the second classical party encodes the pulse and returns it to the first classical party for measurement, thereby realizing information transmission. The actual bidirectional system has more security vulnerabilities. Compared with unidirectional communication, Eve can initiate more side-channel attacks in the bidirectional system by using the photon return process, which is called Trojan horse attack. The present application encodes the bits of unidirectional transmission, and the returned bits detect eavesdropping, thereby solving the security vulnerabilities in the bidirectional system.

[0028] In step 13, if the node state is that the device is not trusted, the nodes in the hybrid networking adopt the double-field semi-quantum key distribution protocol for key distribution.

[0029] Specifically, if the measurement device is not trusted and the information transmission distance is long, the double-field semi-quantum key distribution protocol is selected, i.e., switching to the "both sides to the middle" mode, forming a network of untrusted nodes, and the process is as shown in Figure 3 In this mode, through time reversal, the two classical parties act as two sending ends, and the quantum party acts as a receiving and measuring end. The two classical parties share a segment of the same secure key according to the Bell state measurement result announced by the quantum party. The measurement result of the quantum party does not affect the security of the communication, i.e., the untrusted node networking is realized. Specifically, the two classical parties randomly prepare a coherent state |a> with a fixed phase and a vacuum state |0>, encode each photon by sending and not sending, and send them to the quantum party. The quantum party performs interference measurement on the received pulses. For non-interference measurement results, only whether the photon is received and sent is used as the basis for judging the key value. The double-field semi-quantum key distribution protocol does not require randomization of the phase of the light pulse.

[0030] In one specific application example, step 13 includes steps 31 to 34.

[0031] Step 31, weak coherent states and vacuum states are prepared by two classical parties, and each photon is encoded and sent to the quantum party. Among them, the two classical parties choose to send weak coherent states or vacuum states to the quantum party. Encoding 1 means sending weak coherent states with fixed phase. Encoding 0 means sending vacuum states.

[0032] Step 32, each photon received by the quantum party is interferometrically measured.

[0033] If two classical parties choose to send weak coherent states at the same time, single-photon interference occurs at the quantum party, that is, the first detector of the quantum party responds to interference, and the second detector does not respond to interference.

[0034] If one classical party chooses to send weak coherent states and the other chooses to send vacuum states, no single-photon interference occurs at the quantum party, that is, the first detector and the second detector respond probabilistically, and the second detector is an encoding mode detector. If two classical parties choose to send vacuum states at the same time, the quantum party cannot detect photons.

[0035] Step 33, 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.

[0036] Step 34, if the measurement result is interference, the two classical parties detect eavesdropping according to the interference response result.

[0037] Single-photon interference results in the first detector of the quantum party responding to interference and the second detector not responding to interference. The interference result is used to detect eavesdropping, and the response result of the second detector is used to determine that the encoding of the two classical parties is opposite in this round of communication. The non-interference of two signal lights will cause the first detector and the second detector to respond probabilistically, and the second detector is an encoding mode detector. The two classical parties identify the valid event of no interference and obtain the original key corresponding to each photon according to the response of the second detector from the encoding mode.

[0038] In the double-field semi-quantum key distribution protocol, only whether a photon is received or transmitted is used as the basis for determining the key value, and only a single detector responds. When the encoding mode detector responds, the encoding of the two classical parties is in an anti-correlation relationship, but the quantum party cannot know whether the encoding of the two classical parties is 0 or 1, so the security of the double-field semi-quantum key distribution protocol is measurement-device-independent. The effective detection used by the quantum party to form the code each time only consumes one photon, and the photon only experiences a single side channel, which can break through the coding rate linear limit without quantum relay, and is more suitable for long-distance transmission scenarios.

[0039] In the key distribution process by using the double-field semi-quantum key distribution protocol, the key can be distributed only when no interference occurs between the signal light transmitted by the two classical parties, and the corresponding signal encoding of the two classical parties is reserved as the key according to the valid events of no interference published by the quantum party. The valid events are only single-photon response events, so the code rate and key rate are relatively high, and the security advantage of measurement-device-independent is achieved, and the transition from the trusted node networking to the untrusted node networking is realized.

[0040] In summary, the time reversal is used in the application, the two modes of "sending from the middle to the two ends" and "sending from the two ends to the middle" can be switched, and different communication protocols can be realized in the same system. According to different application scenarios, whether the device is trusted or not, the two communication protocols are switched by the non-independent networking technology, and the one-way code semi-quantum key distribution protocol and the double-field semi-quantum key distribution protocol can be supported in the same system, and the transition from the trusted node to the untrusted hybrid networking is realized.

[0041] Based on the same inventive concept, the application also provides a system for implementing the above-mentioned method. The implementation scheme of the system for solving the problem is similar to the implementation scheme described in the above method, so the specific limitations in one or more system embodiments provided below can refer to the limitations of the method in the above text, and will not be repeated here.

[0042] In an exemplary embodiment, as shown in Figure 4 A semi-quantum key distribution system suitable for hybrid networking is provided, including 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 with the quantum party Charlie through the first quantum channel 123, and the second classical party Bob is connected with the quantum party Charlie through the second quantum channel 124.

[0043] When the node state in the hybrid networking is that the device is trusted, the quantum party Charlie is used to distribute the key to the two classical parties.

[0044] When the node state in the hybrid networking is that the device is untrusted, the first classical party Alice and the second classical party Bob are used to send weak coherent states or vacuum states to the quantum party Charlie. The quantum party Charlie is used to perform interference measurement on the received photons. The first classical party Alice and the second classical party Bob are also used to obtain the key according to the valid events of no interference.

[0045] The semi-quantum key distribution system provided by the application can realize two communication modes, including a one-way code generation semi-quantum key distribution protocol and a two-field semi-quantum key distribution protocol. In the case of coexistence of the two communication modes, one of the two communication modes can be selected for communication according to application requirements, or the two communication modes can be simultaneously communicated to realize mixed networking of trusted nodes and untrusted nodes. When different communication modes are selected, individual devices of the two classical parties are different in function.

[0046] The quantum party Charlie connects the first classical party Alice and the second classical party Bob by using a Michelson interferometer. On one hand, the first classical party Alice and the second classical party Bob code generate by using the one-way code generation semi-quantum key distribution protocol to realize trusted node networking. On the other hand, the first classical party Alice and the second classical party Bob code multiply by using the two-field semi-quantum key distribution protocol with the quantum party Charlie to realize untrusted node networking. The application simultaneously supports the one-way code generation semi-quantum key distribution protocol and the two-field semi-quantum key distribution protocol, realizes mixed networking from trusted nodes to untrusted nodes, and greatly improves the overall practicability and security of the semi-quantum communication network.

[0047] In a specific application example, the quantum party 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.

[0048] The first port of the first circulator 102 is connected with the first detector 103, the second port of the first circulator 102 is connected with the first port of the first beam splitter 105, and the third port of the first circulator 102 is connected with the exit port of the first light source 101.

[0049] The second port of the first beam splitter 105 is connected with the second detector 104, the third port of the first beam splitter 105 is connected with the input port of the first quantum channel 123, and the fourth port of the first beam splitter 105 is connected with the input port of the second quantum channel 124.

[0050] In a specific application example, the first classical party 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.

[0051] One end of the first polarization rotator 106 is connected with the output port of the first quantum channel 123.

[0052] The first port of the second beam splitter 107 is connected with the other end of the first polarization rotator 106, the second port of the second beam splitter 107 is connected with the first port of the second circulator 109, the third port of the second beam splitter 107 is connected with the first port of the first phase modulator 108, and the fourth port of the second beam splitter 107 is connected with the second port of the first phase modulator 108.

[0053] The second port of the second circulator 109 is connected with the second light source 110, and the third port of the second circulator 109 is connected with the first port of the first polarization beam splitter 111 (specifically, the first port of the combination of the first polarization beam splitter 111 and the first optical delay coil 121). The second port of the first polarization beam splitter 111 is connected with the third detector 112, and the third port of the first polarization beam splitter 111 is connected with the third detector 112 through the first optical delay coil 121.

[0054] When the node in the hybrid network is in a device-trusted state, the Sagnac loop interferometer formed by the second beam splitter 107 and the first phase modulator 108 constitutes a first optical switch, and the return or measurement operation of the pulse is realized. When the node in the hybrid network is in a device-untrusted state, the Sagnac loop interferometer formed by the second beam splitter 107 and the first phase modulator 108 constitutes a first intensity modulator, and the operation of transmitting or not transmitting the pulse is realized.

[0055] In one specific application example, the second classical party 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.

[0056] One end of the second polarization rotator 113 is connected with the output port of the second quantum channel 124.

[0057] The first port of the third beam splitter 114 is connected with the other end of the second polarization rotator 113, the second port of the third beam splitter 114 is connected with the first port of the third circulator 116, the third port of the third beam splitter 114 is connected with the first port of the second phase modulator 115, and the fourth port of the third beam splitter 114 is connected with the second port of the second phase modulator 115.

[0058] The second port of the third circulator 116 is connected with the third light source 117, and the third port of the third circulator 116 is connected with the first port of the second polarization beam splitter 118 (specifically, the first port of the combination of the second polarization beam splitter 118 and the second optical delay coil 122). The second port of the second polarization beam splitter 118 is connected with the fourth detector 119. The third port of the second polarization beam splitter 118 is connected with the fourth detector 119 through the second optical delay coil 122.

[0059] When the node state in the mixed networking is that the device is trusted, the Sagnac loop interferometer composed of the third beam splitter 114 and the second phase modulator 115 constitutes a second optical switch, so as to realize the return or measurement operation of the pulse. When the node state in the mixed networking is that the device is untrusted, the Sagnac loop interferometer composed of the third beam splitter 114 and the second phase modulator 115 constitutes a second intensity modulator, so as to realize the operation of transmitting the pulse or not transmitting the pulse.

[0060] In the present application, the intensity modulator is used to realize high-speed intensity modulation, generate weak coherent states and vacuum states for coding. The optical switch (including the first optical switch and the second optical switch) and the intensity modulator (including the first intensity modulator and the second intensity modulator) have the same optical path structure, but have different functions. When switched to the unidirectional coding semi-quantum key distribution protocol, the optical switch function can be realized. When switched to the double-field semi-quantum key distribution protocol, the intensity modulator function can be realized, and high integration can be realized.

[0061] Among them, the transmittance and reflectance ratio of the first beam splitter 105, the second beam splitter 107 and the third beam splitter 114 are all 50:50.

[0062] The working process of the semi-quantum key distribution system suitable for mixed networking provided in the present application is introduced below.

[0063] 1) For trusted node networking, that is, the node state in the mixed networking is that the device is trusted.

[0064] In the trusted quantum party Charlie, the first light source 101 is used to randomly prepare a weakly coherent state polarized in horizontal or vertical direction, wherein the weakly coherent state polarized in horizontal direction is coded as 0, and the weakly coherent state polarized in vertical direction is coded as 1. The prepared signal light is sent to the third port of the first circulator 102, and the signal light is emitted from the second port of the first circulator 102, and then is incident on the first port of the first beam splitter 105, and is split into two sub-pulses, which are respectively emitted from the third port and the fourth port of the first beam splitter 105. The two sub-pulses enter the first classical party Alice and the second classical party Bob respectively. The first classical party Alice and the second classical party Bob respectively use the first optical switch and the second optical switch to randomly select the return or measurement operation of the entering pulse.

[0065] In the present embodiment, the first optical switch can control the opening and closing of the first phase modulator 108. After the sub-pulse entering the first classical party Alice is incident on the first port of the second beam splitter 107, it is again split into two sub-pulses, which are respectively emitted from the third port and the fourth port of the second beam splitter 107. If the phase is adjusted to 0 by the first phase modulator 108, the two sub-pulses interfere at the second beam splitter 107, and finally are emitted from the first port of the second beam splitter 107, which corresponds to the first optical switch being closed, i.e. the first classical party Alice returns the photon. If the phase is adjusted to π by the first phase modulator 108, the two sub-pulses interfere at the second beam splitter 107 and change the emission direction of the pulse, and finally are emitted from the second port of the second beam splitter 107, which corresponds to the first optical switch being opened, i.e. the first classical party Alice measures the photon. The second optical switch follows the same working principle as the first optical switch.

[0066] If the first classical party Alice and the second classical party Bob close the optical switch, the return pulse operation is selected. Closing the first optical switch and the second optical switch at the same time will cause the two sub-pulses to return to the trusted quantum party Charlie along the original path. After the two returned pulses pass through the first polarization rotator 106 and the second polarization rotator 113 and are randomly flipped, the quantum party Charlie measures the returned photon. The quantum party Charlie detects the eavesdropping according to the interference result.

[0067] Again, the two sub-pulses are incident on the third port and the fourth port of the first beam splitter 105 and interfere, and finally are emitted from the first port of the first beam splitter and reach the second port of the first circulator 102, and are emitted from the first port thereof and cause the first detector 103 to respond. The interference result of the detection is used to detect whether there is eavesdropping. The principle of the second classical party Bob and the first classical party Alice selecting the measurement pulse operation is the same.

[0068] If the first classical party Alice opens the first optical switch, the corresponding selection measurement pulse operation is selected, the first optical switch sends the sub-pulse to the first port of the first polarization beam splitter 111, and the first polarization beam splitter 111 finally sends different polarization state pulses to the third detector 112 to cause its response. Among them, if the sub-pulse is horizontally polarized light, it is emitted from the second port thereof; if the sub-pulse is vertically polarized light, it is emitted from the third port thereof and passes through the first optical delay coil 121, the purpose of which is to make the time of arrival of pulses of different polarization states different, realizing time distinguishability, to realize the function of distinguishing pulses of different polarization states. The principle of the selection measurement pulse operation selected by the second classical party Bob is the same as that of the first classical party Alice.

[0069] In the above case, if the first classical party Alice selects to return the photon, the second classical party Bob selects to measure and obtain the photon, and determines the polarization state of the photon according to the measurement result, the quantum bit utilization efficiency of this case is 12.5%; if the second classical party Bob selects to return the photon, the first classical party Alice selects to measure and obtain the photon, and determines the polarization state of the photon according to the measurement result, the quantum bit utilization efficiency of this case is 12.5%; if the first classical party Alice and the second classical party Bob simultaneously select to measure the photon, one of them obtains the photon, and determines the polarization state of the photon according to the measurement result, the quantum bit utilization efficiency of this case is 25%; the quantum bit utilization efficiency of this protocol reaches 50%.

[0070] 2) For untrusted node networking, that is, the node state in hybrid networking is device untrusted.

[0071] By time reversal, the first classical party Alice and the second classical party Bob send quantum bits as senders. Among them, the first classical party Alice or the second classical party Bob sends a weak coherent state encoding as 1, and the first classical party Alice or the second classical party Bob sends a vacuum state encoding as 0. The first classical party Alice prepares a weak coherent state through the second light source 110; the second classical party Bob prepares a weak coherent state through the third light source 117, and the two signal lights are respectively incident from the second port of the second optical circulator 109 and the second port of the third optical circulator 116, and are respectively incident into the first intensity modulator and the second intensity modulator after being emitted from the first port. The first classical party Alice and the second classical party Bob respectively use the first intensity modulator and the second intensity modulator to realize the operations of sending and not sending.

[0072] In the embodiment, the first intensity modulator can modulate the intensity of the signal light by regulating the first phase modulator 108. After the weak coherent state prepared by the first classical party Alice is incident from the second port of the second beam splitter 107, it is again split into two sub-pulses from the third port and the fourth port of the second beam splitter 107. If the phase is regulated to 0 by the first phase modulator 108, the two sub-pulses interfere at the second beam splitter 107, and finally exit from the second port of the second beam splitter 107, corresponding to the first classical party Alice sending a vacuum state; if the phase is regulated to π by the first phase modulator 108, the two sub-pulses interfere at the second beam splitter 107 and change the direction of the exit pulse, and finally exit from the first port of the second beam splitter 107, corresponding to the first classical party Alice sending a weak coherent state. The second intensity modulator follows the same working principle as the first intensity modulator.

[0073] If the first classical party Alice and the second classical party Bob simultaneously select to send a weak coherent state, the two signal lights interfere after being incident from the third port and the fourth port of the first beam splitter and then exit from the first port of the first beam splitter to the second port of the first circulator 102, and finally exit from the first port thereof and cause the first detector 103 to respond, and the interference result of the detection is used to detect whether there is eavesdropping.

[0074] If the first classical party Alice selects to send a weak coherent state and the second classical party Bob selects to send a vacuum state, or the first classical party Alice sends a vacuum state and the second classical party Bob selects to send a weak coherent state, the two signal lights sent by the first classical party Alice and the second classical party Bob are incident from the third port and the fourth port of the first beam splitter respectively but do not interfere, but exit from the first port or the second port of the first beam splitter 105, causing the first detector 103 or the second detector 104 to respond probabilistically.

[0075] If the second detector 104 responds, it indicates that one of the first classical party Alice and the second classical party Bob selects a weak coherent state and the other selects to send a vacuum state. Only when the signal lights sent by the first classical party Alice and the second classical party Bob do not interfere can the key be distributed. According to the effective events of non-interference announced by the quantum party Charlie, the first classical party Alice and the second classical party Bob will correspondingly encode the signal to keep it as a key, and one of the two classical parties flips its own bits to share the key with the other party.

[0076] The application realizes time reversal of the execution process of the semi-quantum key distribution protocol, two classical parties as the sender send the prepared signal light corresponding to the emission and non-emission of the photon according to the measurement, and then send it to the quantum party Charlie. The quantum party Charlie performs Bell state measurement on the photons sent by the two classical parties, identifies the effective detection event without interference, and only needs a single detector response. The two classical parties are encoded into an anti-correlation relationship, but the quantum party Charlie cannot know whether the encoding of the two classical parties is 0 or 1, so the double-field semi-quantum key distribution protocol can be realized. This process can be implemented in the same system to implement different protocol schemes, that is, the two communication protocols of the one-way coding semi-quantum key distribution'middle to both sides' and the double-field interference semi-quantum key distribution 'both sides to the middle' are switched.

[0077] In summary, compared with the prior art, the application has at least the following beneficial effects: (1) Improve the security: the one-way coding semi-quantum key distribution protocol solves the security risks of the two-way system by reducing the assumption of the source quantum state and by returning the bit detection eavesdropping through one-way transmission of bits. The double-field semi-quantum key distribution protocol uses the principle of single-photon interference to create entangled states between the two communicating parties through post-selection, thereby completing the generation of the key. This design inherits the basic architecture of the measurement-device-independent protocol and has extremely high security.

[0078] (2) Improve the performance: in the one-way coding semi-quantum key distribution protocol, the quantum party Charlie sends the key to the two classical parties at the same time, and the quantum bit utilization efficiency reaches 50%, which is twice the quantum bit utilization efficiency of the BB84 protocol; the double-field semi-quantum key distribution protocol can extend the distance of semi-quantum key distribution to a certain extent, which is helpful for realizing inter-city network interconnection.

[0079] It should be noted that the user information (including but not limited to user equipment information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of related data need to comply with relevant regulations.

[0080] In the application, all actions of obtaining signals, information or data are performed under the premise of complying with the corresponding data protection regulations and policies of the place of residence, and under the premise of obtaining authorization from the owner of the corresponding device.

[0081] Any technical features in the above embodiments can be combined, and for the sake of brevity, not all possible combinations are described above, however, it should be understood that the application encompasses all possible combinations of the technical features described above.

[0082] The principles and implementation manners of the present application are described herein by using specific examples, and the above embodiments are only used to help understand the method of the present application and its core idea; meanwhile, according to the idea of the present application, the specific implementation manners and application scopes will be changed by those skilled in the art. In conclusion, the content of the present specification should not be understood as a limitation of the present application.

Claims

1. A semi-quantum key distribution method suitable for hybrid networking, characterized in that, The method comprises: determining a node state in a mixed network; the node state is device trusted or device untrusted; if the node state is device trusted, a node in the mixed network adopts a one-way code construction semi-quantum key distribution protocol to distribute keys; if the node state is device untrusted, the node in the mixed network adopts a two-field semi-quantum key distribution protocol to distribute keys; the node in the mixed network comprises one quantum party and two classical parties; the one-way code construction semi-quantum key distribution protocol distributes keys for the quantum party to the two classical parties; the two-field semi-quantum key distribution protocol sends a coherent state or a vacuum state for the quantum party from the two classical parties, and the two classical parties obtain keys according to effective events without interference.

2. The semi-quantum key distribution method suitable for hybrid networking according to claim 1, wherein, The node in the mixed network adopts the one-way code construction semi-quantum key distribution protocol to distribute keys, specifically comprising: preparing a weak coherent state by a quantum party, and encoding the polarization of each photon to divide into two pulses, which are sent to two classical parties respectively; the two classical parties randomly select returned photons or measured photons; if the two classical parties simultaneously select returned photons, the polarization direction of the photon is randomly flipped when returned; interference measurement is performed on the returned photon of the classical party by the quantum party to obtain an interference measurement result to detect eavesdropping; if any classical party selects a measured photon, the photon is obtained by measuring the classical party to determine the polarization state of the photon, and the key sent by the quantum party is obtained according to the polarization state of the photon.

3. The semi-quantum key distribution method suitable for hybrid networking according to claim 1, wherein, The node in the mixed network adopts the two-field semi-quantum key distribution protocol to distribute keys, specifically comprising: randomly preparing a weak coherent state and a vacuum state by two classical parties, and encoding each photon to send to a quantum party; interference measurement is performed on each received photon by the quantum party; if the measurement result is no interference, the two classical parties identify effective events without interference to obtain the key corresponding to each photon; if the measurement result is interference, the two classical parties detect eavesdropping according to the interference response result.

4. The semi-quantum key distribution method suitable for hybrid networking according to claim 3, wherein, if the two classical parties simultaneously select to send a weak coherent state, the measurement result is interference; if one classical party selects to send a weak coherent state and the other classical party selects to send a vacuum state, the measurement result is no interference; if the two classical parties simultaneously select to send a vacuum state, the quantum party cannot detect the photon.

5. A semi-quantum key distribution system suitable for hybrid networking, characterized by, The system is applied to the semi-quantum key distribution method for a mixed network in any one of claims 1-4, and the system comprises 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 with the quantum party through the first quantum channel, and the second classical party is connected with the quantum party through the second quantum channel; when the node state in the mixed network is device trusted, the quantum party is used to distribute keys for the two classical parties. When the node state in the mixed networking is device untrusted, the first classical party and the second classical party are configured to send weak coherent states or vacuum states to the quantum party; the quantum party is configured to perform interferometric measurement on the received photons; and the first classical party and the second classical party are further configured to obtain a key according to valid events without interference.

6. The semi-quantum key distribution system suitable for hybrid networking according to claim 5, wherein, The quantum party comprises 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 with the first detector, the second port of the first circulator is connected with the first port of the first beam splitter, and the third port of the first circulator is connected with the exit port of the first light source; The second port of the first beam splitter is connected with the second detector, the third port of the first beam splitter is connected with the input port of the first quantum channel, and the fourth port of the first beam splitter is connected with the input port of the second quantum channel.

7. The semi-quantum key distribution system suitable for hybrid networking according to claim 5, wherein, The first classical party comprises 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 with the output port of the first quantum channel; The first port of the second beam splitter is connected with the other end of the first polarization rotator, the second port of the second beam splitter is connected with the first port of the second circulator, the third port of the second beam splitter is connected with the first port of the first phase modulator, and the fourth port of the second beam splitter is connected with the second port of the first phase modulator; The second port of the second circulator is connected with the second light source, and the third port of the second circulator is connected with the first port of the first polarization beam splitter; the second port of the first polarization beam splitter is connected with the third detector, and the third port of the first polarization beam splitter is connected with the third detector through a first optical delay coil.

8. The semi-quantum key distribution system suitable for hybrid networking according to claim 7, wherein, When the node state in the mixed networking is device trusted, the Sagnac loop interferometer formed by the second beam splitter and the first phase modulator constitutes a first optical switch, and the return or measurement operation of the pulse is realized; When the node state in the mixed networking is device untrusted, the Sagnac loop interferometer formed by the second beam splitter and the first phase modulator constitutes a first intensity modulator, and the operation of sending or not sending the pulse is realized.

9. The semi-quantum key distribution system suitable for hybrid networking according to claim 5, wherein, The second classical party comprises 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 with the output port of the second quantum channel; The first port of the third beam splitter is connected with the other end of the second polarization rotator, the second port of the third beam splitter is connected with the first port of the third circulator, the third port of the third beam splitter is connected with the first port of the second phase modulator, and the fourth port of the third beam splitter is connected with the second port of the second phase modulator; The second port of the third circulator is connected with the third light source, and the third port of the third circulator is connected with the first port of the second polarization beam splitter; the second port of the second polarization beam splitter is connected with the fourth detector; and the third port of the second polarization beam splitter is connected with the fourth detector through a second optical delay coil.

10. The semi-quantum key distribution system suitable for hybrid networking according to claim 9, wherein, When the node state in the mixed networking is device trusted, a second optical switch is formed based on the Sagnac loop interferometer of the third beam splitter and the second phase modulator, so as to realize return or measurement operation of the pulse; When the node state in the mixed networking is device untrusted, a second intensity modulator is formed based on the Sagnac loop interferometer of the third beam splitter and the second phase modulator, so as to realize sending pulse or not sending pulse operation.

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