Quantum key distribution method and system based on pattern pairing and passive decoy state

Abstract

The invention belongs to the technical field of quantum communication, and particularly relates to a quantum key distribution method and system based on mode pairing and a passive decoy state. In order to overcome the defect that the problem of side channel information leakage possibly exists due to the fact that an active decoy state method is adopted in an existing quantum key distribution method based on mode pairing, the invention adopts the following technical scheme that the quantum key distribution method based on mode pairing and passive decoy state comprises the following steps: two parties respectively generate a pair of entangled photons; the two parties respectively carry out information coding on signal photons through a signal path and a decoy path to obtain a coherent quantum state, and randomly send a modulated signal state or decoy state to Charlie; the Charlie performs single-photon interference measurement on the coherent quantum states sent by the two parties and publishes a measurement result; repeating for N rounds and then carrying out mode pairing; screening basis vectors; key mapping; estimating parameters; and key extraction. The method has the beneficial effects that the security is improved while a relatively high key generation rate is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum communication, and particularly relates to a quantum key distribution method and system based on mode pairing and passive decoy states. Background Art

[0002] The power communication network is an integral part of the power system, and the secure operation of the power communication network is the guarantee for the stable operation of the power system. The operation, control instructions, and enterprise services of the power system involve a large amount of private data, and have high requirements for real-time performance and security levels. Therefore, the power system builds a dedicated power network to ensure data communication security. With the development of information technology, dedicated networks may also be invaded, and power system attacks occur from time to time. Therefore, how to ensure the operation security of the power system has become an important research topic.

[0003] Applying new quantum cryptography technologies to ensure the security of the power communication network is one of the important research directions. Quantum Key Distribution (QKD) technology (also known as the QKD protocol) is one of the most invested and studied directions in current quantum cryptography. Different from other cryptography technologies, the QKD protocol uses the characteristics of quantum states to ensure the security of the key distribution process, realizes absolute security proven by information theory in the case of one-time pad encryption, and can effectively resist attacks under the ultra-high parallel computing power of quantum computing.

[0004] A common quantum key distribution method is Measurement-Device-Independent Quantum Key Distribution (MDI-QKD). Both communication parties A and B are senders, and simultaneously send coherent optical pulses in a fixed pairing manner to an untrusted measurement device C in the channel. A pair of coherent optical pulses corresponds to a single-photon signal. C announces the interference results of the two single-photon signals sent by A and B to assist A and B in generating keys. Among them, during the transmission of each pair of coherent optical pulses, if one of the coherent optical pulses is lost, this pair of coherent optical pulses cannot be used to generate keys, thereby causing the number of single-photon signals used to generate keys to decrease accordingly. Therefore, there is a problem of low key generation rate.

[0005] In 2022, the team of Professor Maxiong Feng proposed a Mode Pairing Quantum Key Distribution (MP-QKD) protocol. By combining two successful events with successful detections in the original dual-field protocol into a pair, it achieved two-mode interference, effectively reducing the technical complexity of the experiment. For reference, see CN112491536A. However, MP-QKD uses a weak coherent light source as the signal light source, and the single-photon component is relatively small, resulting in a large limitation on the key rate.

[0006] At the same time, existing mode pairing quantum key distributions do not involve decoy states. When using the traditional active decoy state method, there may be a problem of side-channel information leakage. Although active modulation (active decoy state) can well implement the MP-QKD protocol, in some special scenarios, a passive decoy state method is still required. For example, when the intensity modulator is defective, some side information will be introduced during the preparation of the decoy state, and at this time, the active modulation of the main pair pulse intensity may lead to serious security problems. Summary of the Invention

[0007] Aiming at the deficiency that the existing quantum key distribution method based on mode pairing using the active decoy state method may have the problem of side-channel information leakage, the present invention provides a quantum key distribution method based on mode pairing and passive decoy state, which uses a labeled paired coherent light source with a higher single-photon component to replace the weak coherent light source to obtain a higher key generation rate; a passive decoy state module is placed at the Alice end and the Bob end to avoid information leakage in the side channels of the network, so that when Alice and Bob randomly select decoy state pulses, they can passively select decoy states of different modes according to the response results of their local detectors, increasing security. The present invention also provides a quantum key distribution system based on mode pairing and passive decoy state.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A quantum key distribution method based on mode pairing and passive decoy state, the quantum key distribution method based on mode pairing and passive decoy state includes the following steps: S1. Alice and Bob respectively generate a pair of entangled photons, where the idle photons are received by the local first detector, and the signal photons are sent to the passive decoy state module; S2. Alice and Bob respectively encode the information of the signal photons through two paths, the signal path and the decoy path, to obtain coherent quantum states A i and B i , and randomly send the modulated signal state or decoy state to Charlie; S3. Charlie performs on the coherent quantum states sent by Alice and BobA i and B i Perform single - photon interference measurement and announce the measurement results. Among them, the situation where only one of Charlie's two detectors responds is called a successful detection; S4. After repeating N rounds of S1 to S3, perform mode pairing; S5. Basis vector screening: Determine and screen the type of basis according to the intensities selected by Alice and Bob in the two paired rounds; S6. Key mapping: Alice and Bob respectively determine the initial key according to the basis, intensity, and phase of each pair; S7. Parameter estimation; S8. Key extraction.

[0009] As an improvement, in S2, after the signal passes through a beam splitter of the first passive decoy state module, it enters the signal path and the decoy path respectively and is modulated. After the modulated signal passes through the second beam splitter, one path is sent to Charlie, and the other path reaches the two local detectors of Alice or Bob through the third beam splitter; For the i round quantum state of Alice, its coherent quantum state is expressed as A i , where the superscript represents the Alice side, is the intensity of the coherent state, is the phase of the coherent state, , and is the imaginary unit; If the signal state is sent, the intensity is randomly selected from {0, μ}, and at the same time the phase is randomly selected from [0, 2π), and the intensity of the decoy path is modulated to zero; If the decoy state is sent, the variable attenuator of the decoy path remains unmodulated, and the intensity is randomly selected from {0, μ}, and the pulse phases on both paths are randomly selected from [0, 2π); Alice obtains different decoy state patterns according to the response results of the second and third local detectors and gets the decoy state pulse phase .

[0010] As an improvement, in S2, according to the response results of the second and third local detectors of Alice, the detection events are divided into four categories: neither responds, the first responds and the second does not respond, the first does not respond and the second responds, and both respond; The probabilities of the four - type response events are:

[0011] is the photon number distribution with an average photon number of , is the probability of the occurrence of one of the four types of detection events, represents the four types of detection events, , n is the number of photon states; The probability that the photon state projects onto Alice's local second and third detectors is expressed as: is expressed as:

[0012] where, is the transmittance coefficient of the third beam splitter , and are the detection efficiencies of the local second and third detectors respectively.

[0013] As an improvement, in S2, when the dark counts of Alice's three detectors are the same, i.e., , and the detection efficiencies are also the same, i.e., , the photon number occurrence probabilities of the four types of events are:

[0014] where, is the transmittance of the third beam splitter. When the transmittance of the third beam splitter is 0.5, then in the above formula is the same as .

[0015] As an improvement, in S4, when both Alice and Bob send signal states, for all successful detection rounds, Alice and Bob combine two successful detection rounds with an interval not exceeding the maximum pairing interval into a pair, and form a data pair with the encoding phases or intensities in these two rounds.

[0016] As an improvement, in S5, if for two paired successful rounds, the intensities selected by Alice are (0, μ) or (μ, 0), Alice marks the data pair as the Z basis; if the intensity is (μ, μ), it is marked as the X basis; if the intensity is (0, 0), it is marked as the 0 basis; Bob uses the same method to set the basis of the data pair; after the basis setting is completed, Alice and Bob announce the basis of each data pair. If both announce the X basis or the Z basis, it is retained, otherwise it is discarded.

[0017] As an improvement, in S6, for each Z-basis data pair with index values of i and j if the intensity of Alice ([[]] , ) = (0, μ ), then Alice sets her key to 0, otherwise sets to 1; Bob's initial key bit setting is just the opposite of Alice's, that is, Bob's strength( , ) = (0, μ ), sets his key to 1, otherwise sets to 0; For X - basis data pairs, the initial key is obtained from the relative phase, and the calculation formula is:

[0018]

[0019] ; Bob determines the initial key bit k b and the alignment angle θ b in a similar way, but Bob has an additional key - flipping operation: if in two rounds, the detector responses of the i and the j are (L, L) or (R, R), then Bob keeps his key bit; if the detector responses are (L, R) or (R, L), then Bob flips the key bit, and in the X - basis, only when the alignment angles of Alice and Bob are equal, that is θ a = θ b will the data pair be kept, otherwise the data pair will be discarded.

[0020] As an improvement, in S7, Alice and Bob perform parameter estimation on the phase - flip error rate and qubit error rate of the Z - basis.

[0021] As an improvement, in S8, Alice and Bob use the Z - basis pairs in the case of the sent signal states to generate keys, and at the same time, according to , and carry out key negotiation and privacy amplification to obtain secure keys; The expression formula for the key generation rate is:

[0022] Among them, , representing the expected value of the number of pairs generated per round, lis the maximum pairing interval, p is the probability that a certain round is a successful detection event, r s is the probability that a successful detection pulse pair is a signal pair, and are respectively the expected single - photon pair example and the phase error rate of single - photon pairs in the signal pair, f is the error - correction efficiency, is the bit error rate of the signal pair, is the binary Shannon entropy function.

[0023] A quantum key distribution system based on mode pairing and passive decoy states includes two communication devices and a measurement device for performing the aforementioned quantum key distribution method based on mode pairing and passive decoy states. The measurement device is communicatively connected to the two communication devices respectively, and the two communication devices are communicatively connected to each other.

[0024] The quantum key distribution method based on mode pairing and passive decoy states of the present invention, on the basis of the existing mode - pairing quantum key distribution protocol, replaces the weak coherent light source with a labeled paired coherent light source with a higher single - photon component as the signal light source at the Alice and Bob ends to obtain a higher key generation rate. At the same time, passive decoy - state devices are placed at the Alice and Bob ends to avoid information leakage in the side channels of the network, so that when Alice and Bob randomly select decoy - state pulses, they can passively select different - mode decoy states according to the response results of their respective local detectors, thereby increasing security. Therefore, the present invention has the following advantages: (1) It is an extension of the mode - pairing quantum key distribution method, and its key generation rate can break through the linear key - rate bound; (2) Compared with the original mode - pairing quantum key distribution protocol under the same conditions, it has a higher key generation rate and a longer transmission distance; (3) Adopting the mode - pairing strategy, global phase locking is not required during implementation, reducing the experimental technical difficulty; (4) Adopting the passive decoy - state method, it avoids additional information leakage in the side channels and improves the security of the quantum key distribution protocol; (5) It can be implemented with off - the - shelf optical devices and has great application prospects in the power communication scenario. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the architecture diagram of the quantum key distribution system based on mode pairing and passive decoy states according to an embodiment of the present invention.

[0026] Figure 2 is the flowchart of the quantum key distribution method based on mode pairing and passive decoy states according to an embodiment of the present invention.

[0027] Figure 3 is the simulation result diagram of the quantum key distribution method based on mode pairing and passive decoy states according to an embodiment of the present invention. Detailed implementation manners

[0028] The technical solutions of the embodiments of the present invention will be explained and described below. However, the following embodiments are only the preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation manners without creative efforts fall within the protection scope of the present invention.

[0029] See Figure 1 , the quantum key distribution system based on pattern pairing and passive decoy states in the embodiment of the present invention includes two communication devices Alice and Bob and a measurement device Charlie. The measurement device is respectively communicatively connected to the two communication devices, and the two communication devices are communicatively connected to each other.

[0030] The channels of Alice and Bob to Charlie are symmetric and independently and identically distributed. For the same process of Alice and Bob, only Alice will be described.

[0031] The Alice side includes a heralded pair - coherent source (HPCS), a first detector D1 a , a first beam splitter BS1 a , a variable attenuator on the path S (signal path) and a first phase encoder PM1 a , a variable attenuator on the path D (decoy path) and a second phase encoder PM2 a , a second beam splitter BS2 after the paths S and D converge a , a third beam splitter BS3 a , a second detector D2 a , a third detector D3 a . The signal passing through the second beam splitter BS2 a goes to Charlie along one path, and goes to the second detector D2 a and the third detector D3 a after passing through the third beam splitter BS3 a。

[0032] Charlie has two detectors D L and D R , which respectively detect the signals split by the second beam splitter BS2 a from Alice and Bob.

[0033] See Figure 2 , the quantum key distribution method based on pattern pairing and passive decoy states in the embodiment of the present invention includes: S1. Alice and Bob respectively generate a pair of entangled photons, where the idle photons are received by the local first detector, and the signal photons are sent to the passive decoy state module; S2. Alice and Bob respectively encode information on the signal photons through two paths, the signal path and the decoy path, to obtain a coherent quantum state A i and B i , and randomly send the modulated signal state or decoy state to Charlie; S3. Charlie performs single-photon interference measurement on the coherent quantum states A i and B i sent by Alice and Bob and announces the measurement results. Among them, the situation where only one of Charlie's two detectors responds is called a successful detection; S4. After repeating N rounds of S1 to S3, pattern pairing is performed; S5. Basis vector screening: Determine the type of basis according to the intensities selected by Alice and Bob in the two paired rounds and perform screening; S6. Key mapping: Alice and Bob respectively determine the initial key according to the basis, intensity, and phase of each pair; S7. Parameter estimation; S8. Key extraction.

[0034] In this embodiment, in S1, Alice and Bob respectively generate a pair of entangled photons through the nonlinear crystal of HPCS and enter the idle optical path and the signal optical path respectively. The photons in the idle optical path reach the first detector D1 a , which is used to predict the arrival time of the photons in the signal optical path. Only when the first detector D1 a responds, the pulse modulated by the photons in the signal optical path is used for encoding. The expression of the photon distribution function in the signal pulse emitted by the labeled paired coherent light source is:

[0035] In the formula, is the photon number distribution with an average photon number of (i.e., the photon number distribution in HPCS), represents the average intensity of the signal pulse, n represents the photon number, and are respectively the dark count rate and detection efficiency of the detector, represents the post-selection probability, is the first kind of modified Bessel function.

[0036] The photon number distribution function of a theoretically weak coherent light source is , under the same parameters ( , , η ), the quantity ratios of the photon number pulses of the two light sources are shown in Table 1.

[0037] Table 1 Proportions of vacuum pulses, single-photon pulses and multi-photon pulses in different light sources

[0038] As can be seen from Table 1, compared with the weak coherent light source, the single-photon component in the pulses generated by the labeled paired coherent light source is higher, and the vacuum component is reduced, which is closer to the ideal single-photon source and is beneficial to improving the key generation rate of MP-QKD.

[0039] In this embodiment, in S2, Alice randomly sends a signal state or a decoy state in each round of distribution, and for the i -th round ( i = 1, 2,..., N ), the coherent quantum state is A i , where the superscript represents the Alice side, is the intensity of the coherent state, is the phase of the coherent state, , and is the imaginary unit. The specific distribution process is as follows: If the signal state is sent at this time, the intensity will be randomly selected from {0, μ}, and at the same time the phase will be randomly selected from [0, 2π), that is, the decoy path D is blocked (the variable optical attenuator of the decoy path is modulated to zero), and the phase of the signal state is modulated by the first phase modulator ; If the decoy state is sent at this time, the variable optical attenuator (VOA) of the decoy path D is not modulated, and the intensities of both the signal path and the decoy path are randomly selected from {0, μ} , and the phase modulators and randomly select the phase from [0, 2π) as the pulse phase on both paths; Different decoy state patterns are obtained according to the response results of the local second and third detectors in the passive decoy state module, and the decoy state pulse phase is obtained.

[0040] The specific decoy state patterns are as follows: Alice uses two local detectors ( )Based on the response results, the detection events are classified into four categories, denoted respectively by where event corresponds to neither detector responding, corresponds to responding and not responding, corresponds to responding and not responding, and event corresponds to both detectors responding. If the dark count of the second detector is , the dark count of the third detector is , and the photon number states projected onto and are , then the probabilities of different response events of the local detector can be calculated as shown in Table 2.

[0041] Table 2 Probabilities of Different Events

[0042] For any photon state, the probability projected onto can be expressed as:

[0043] where is the transmittance coefficient of the third beam splitter , and are the detection efficiencies of the second detector and the third detector respectively. On this basis, the probability of the response event can be obtained as:

[0044] To simplify and without loss of generality, assume that the dark counts of each detector in the system are the same, i.e., , and the detection efficiencies are also the same, i.e., . Then the photon number occurrence probabilities of the 4 events can be obtained as:

[0045] If the transmittance of the beam splitter is 0.5, then in the above formula is the same as .

[0046] Bob performs the same quantum state preparation process as Alice to prepare his coherent quantum state .

[0047] In this embodiment, in S3, Charlie performs single-photon interference measurement on the A i and B i sent by Alice and Bob and announces the measurement results. Among them, the situation where only one of Charlie's two detectors (D L and D R ) responds is called a successful detection. After repeating N rounds, Alice and Bob perform subsequent processing on the obtained data.

[0048] In this embodiment, in S4, when both Alice and Bob send signal states, for all rounds of successful detection, Alice and Bob combine two rounds of successful detection with an interval not exceeding the maximum pairing interval l into a pair, and form a data pair from the encoded phases or intensities in these two rounds. Specifically: (i) First, find the first round of successful detection and record it as the leading pulse; (ii) Search backward for the next round of successful detection. If the interval between the newly found round of successful detection and the existing leading pulse is within the maximum pairing interval l, then set this round as the corresponding trailing pulse and the pairing is successful; otherwise, the pairing fails, discard the existing leading pulse, and set this round as the new leading pulse; (iii) Continue to search backward and repeat steps (i) - (ii) until all pairings are completed.

[0049] In this embodiment, in S5, set the basis according to the intensities of the two rounds i and j that form a pair, including the Z basis, X basis, or 0 basis. If for two paired rounds, the intensities selected by Alice are (0, μ) or (μ, 0), Alice marks the data pair as the Z basis; if the intensity is (μ, μ), it is marked as the X basis; if the intensity is (0, 0), it is marked as the 0 basis. Bob uses the same method to set the basis of the data pair. After the basis setting is completed, Alice and Bob announce the basis of each data pair. If they both announce the X basis or Z basis, it is retained; otherwise, it is discarded.

[0050] In this embodiment, in S6, Alice and Bob respectively determine the initial key according to the basis, intensity, and phase selected for each pair. For each Z - basis data pair with index values i and j, if the intensity selected by Alice = (0, μ), then Alice sets her key to 0; otherwise, it is set to 1; Bob's initial key bit setting is just the opposite of Alice's, that is, if the intensity selected by Bob (,) = (0, μ), he sets his key to 1, otherwise it is set to 0. For X - basis data pairs, the initial key is obtained from the relative phase. From it can be obtained , and ; Bob determines the initial key bit in a similar manner kb and the alignment angle θ b , but Bob has an additional key flipping operation. If in two rounds, the detector responses of the i-th and j-th are (L, L) or (R, R), then Bob keeps his key bit; if the detector responses are (L, R) or (R, L), then Bob needs to flip his key bit, and in the X basis, only when the alignment angles of Alice and Bob are equal ( θ a = θ b ), the data pair will be kept, otherwise the data pair will be discarded.

[0051] In this embodiment, in S7, Alice and Bob perform parameter estimation on the phase flipping error rate and qubit error rate of the Z-basis data.

[0052] In this embodiment, in S8, Alice and Bob use the Z-basis pairs in the case of the transmitted signal state to generate keys. At the same time, they perform key negotiation and privacy amplification according to , and to obtain secure keys.

[0053] Since only the modulation methods of the light source distribution and the decoy state intensity are changed, and aspects such as successful events, pairing strategies, mode pairing, basis vector screening, parameter estimation, and key extraction remain unchanged, the key generation rate formula should be the same as that of the original MP-QKD protocol, expressed as:

[0054] where, , represents the expected value of the number of pairs generated per round, l is the maximum pairing interval, p is the probability that a certain round is a successful detection event, r s is the probability that a successful detection pulse pair is a signal pair, and are respectively the expected single-photon pair ratio and the phase error rate of the single-photon pair in the signal pair, f is the error correction efficiency, is the bit error rate of the signal pair, is the binary Shannon entropy function.

[0055] For the convenience of the subsequent key generation rate analysis, the transmission state of Alice in the i -th round is denoted as , where indicates that the transmitted optical intensity is 0 or μ , is a random phase. Bob's coherent state is denoted as , , is a random phase. Using the array to represent the intensities of Alice and Bob in the i th round.

[0056] For the ( i , j )th pulse pair to be paired, let , where is the modulo-2 addition operation. When , the ( i , j ) pair is set as the Z-basis pair. In the i th round, two variables L i , R i are used to represent the response events of the D i and D L detectors in the R th round. Then the response variable , and the detection probability is expressed as:

[0057] where represents the dark count rate of the detector, is the expression of the photon number distribution function of HPCS, represents the total transmittance of the system, where represents the transmittance of the channel, is the fiber loss system, is the transmission distance, i.e., the distance between Alice and Bob, is the efficiency of the detector.

[0058] The phase-randomized coherent state emitted in the i th round can also be regarded as a mixture of photon number states. represents the detection probability when Alice and Bob emit photon number states of and respectively. This detection probability can be expressed as:

[0059] From formula (2), the probability of successful response of the i th signal is:

[0060] where the signal pairs are independent of each other. After pairing the i th round and the j th round, the probability of successful response in the Z-basis is: 。

[0061] In this embodiment, the passive decoy state module includes a signal path S (including a variable attenuator and a first phase encoder PM1 a ), a decoy path D including a variable attenuator and a second phase encoder PM2 a ), and a second beam splitter BS2 a , a third beam splitter BS3 a and two local single-photon detectors (a second detector D2 a , a third detector D3 a ). Therefore, in the passive decoy state mode, Alice obtains four types of response events according to the response results of the two local detectors (D2 a 、 D3 a ). At the same time, Bob also has four types, so there are many types of situations that cause the two detectors D L and D R at Charlie's end to respond, and there are improvements in the ways and quantities of generating passive decoy states.

[0062] In the passive decoy state mode pairing scheme, when , a successful response will occur. Therefore and (generating a signal pair) have four possible situations: , where cases will result in error codes.

[0063] To simplify the symbolic formulas involved, several events are introduced: 。

[0064] The probability of forming a signal pair is: 。

[0065] The quantum bit error rate of the original key data in the Z-basis pair estimated by Alice and Bob is : 。

[0066] In the decoy state window, according to formula (4), the single-photon contrast ratio in the effective signal pair is estimated to be: 。

[0067] In the mode pairing scheme under passive decoy states, if the decoy state estimation is perfect, the phase error rate is the same as that of the phase-encoding-based MDI-QKD scheme, and the gain and error rate of the X-basis can be directly estimated using the following formulas:

[0068]

[0069] Among them, , e 0 is the error rate caused by background light, e d is the optical error rate caused by imperfect system optical calibration.

[0070] Figure 3 is the simulation result diagram of this embodiment. In the figure, the abscissa is the transmission distance (Transmission distance), the unit is km, the ordinate is the key generation rate (Key generation rate), the red dashed line is the linear secure key rate generation bound (PLOB) without relay, and the black dashed line represents the key generation rate of the method of this embodiment when the maximum pairing distance is 10 2 , the black solid line represents the key generation rate of the method of this embodiment when the maximum pairing distance is 10 3 , the black solid line with circles represents the key generation rate of the method of this embodiment when the maximum pairing distance is 10 4 , the black solid line with * represents the key generation rate of the method of this embodiment when the maximum pairing distance is 10 6 .

[0071] From Figure 3 it can be seen that under the same simulation parameters, as the maximum pairing distance increases, the key generation rate of the method of this embodiment continuously improves. When the maximum pairing distance is greater than 10 3 , the key generation rate of the method of this embodiment can exceed the linear secure key rate generation bound. When the key rate is 10 -8 , under the same simulation parameters, when the maximum pairing distance is 10 3 , the communication distance of the method of this embodiment can reach about 400 km, and when the maximum pairing distance is 10 6 , the communication distance of the method of this embodiment has exceeded 500 km.

[0072] The above analysis results show that when the maximum pairing distance of the method of this embodiment is greater than 10 3 , it can break through the linear limit of the key rate of quantum key distribution, and both its key rate and communication distance are greatly improved.

[0073] Due to the adoption of the passive decoy state method, additional information leakage through side channels is avoided, enhancing the security of the quantum key distribution protocol. Meanwhile, because the mode pairing strategy is employed in the protocol, global phase locking is not required during implementation, reducing the experimental technical difficulty. This is of great significance for applying the new quantum cryptography technology to the operation security guarantee of power systems. Alice obtains four types of response events based on two local detectors. Meanwhile, Bob also has four types, which cause two detectors D L and D R There are many types of response conditions, and there are improvements in the ways and quantities of generating passive decoy states.

[0074] As described above, the above are only specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes but is not limited to the content described in the above specific implementation manners. Any modification that does not deviate from the functional and structural principles of the present invention will be included in the scope of the claims.

Claims

1. A quantum key distribution method based on pattern matching and passive decoy states, characterized in that: The quantum key distribution method based on pattern pairing and passive decoy states includes the following steps: S1. Alice and Bob respectively generate a pair of entangled photons, where the idle photons are received by the local first detector, and the signal photons are sent to the passive decoy state module; S2. Alice and Bob respectively perform information encoding on the signal photons passing through the signal path and the decoy path to obtain coherent quantum states A i and B i , and randomly send the modulated signal states or decoy states to Charlie; S3. Charlie performs single-photon interference measurements on the coherent quantum states sent by Alice and Bob A i and B i announces the measurement results. Among them, the situation where only one of Charlie's two detectors responds is called a successful detection; S4. After repeating N rounds of S1 to S3, pattern pairing is performed; S5. Basis vector screening: Determine the type of basis according to the intensities selected by Alice and Bob in two successful pairing rounds and screen; S6. Key mapping: Alice and Bob respectively determine the initial key according to the basis, intensity and phase of each pair; S7. Parameter estimation; S8. Key extraction.

2. The quantum key distribution method based on pattern matching and passive decoy states according to claim 1, wherein: In S2, after the signal passes through a beam splitter of the passive decoy state module, it respectively enters the signal path and the decoy path and is modulated. After passing through the second beam splitter, one way is sent to Charlie, and the other way reaches the two local detectors of Alice or Bob through the third beam splitter; For the i -th round of quantum state of Alice, its coherent quantum state is expressed as , where the superscript represents the Alice side, is the intensity of the coherent state, is the phase of the coherent state, , and is the imaginary unit; If the transmitted state is a signal state, the intensity is randomly selected from {0, μ}, and at the same time the phase is randomly selected from [0, 2π), and the intensity of the decoy path is modulated to zero; If the sent state is a decoy state, the variable attenuator in the decoy path remains unmodulated, and the intensity is randomly selected from {0, μ}. The pulse phases on both paths are randomly selected from [0, 2π). Alice obtains different decoy state patterns based on the response results of the second and third local detectors, and gets the decoy state pulse phase .

3. The quantum key distribution method based on pattern matching and passive decoy states according to claim 2, wherein: In S2, according to the response results of the local second and third detectors, Alice classifies the detection events into four categories: neither responds, the first responds and the second does not respond, the first does not respond and the second responds, and both respond; The probabilities of the four response events are: is the photon number distribution with an average photon number of , is the probability of the occurrence of one of the four types of detection events, represents the four types of detection events, , n is the number of photon states; The probability that the photon state is projected onto Alice's local second and third detectors is denoted as follows Among them, is the transmittance coefficient of the third beam splitter , and and are the detection efficiencies of the local second and third detectors respectively.

4. The quantum key distribution method based on pattern matching and passive decoy states according to claim 3, wherein: In S2, when the dark counts of Alice's three detectors are the same, i.e., , and the detection efficiencies are also the same, i.e., , the occurrence probabilities of the photon numbers for the four types of events are as follows: Among them, is the transmittance of the third beam splitter. When the transmittance of the third beam splitter is 0.5, then in the above formula is the same as .

5. The quantum key distribution method based on pattern pairing and passive decoy states according to claim 1, characterized in that: In S4, when both Alice and Bob send signal states, for all successfully detected rounds, Alice and Bob combine two successfully detected rounds with an interval not exceeding the maximum pairing interval into a pair, and form a data pair with the coding phase or intensity in these two rounds.

6. The quantum key distribution method based on pattern matching and passive decoy states according to claim 5, characterized in that: In S5, if in two successfully paired rounds, the intensity selected by Alice is (0, μ) or (μ, 0), Alice marks the data pair as the Z basis; if the intensity is (μ, μ), it is marked as the X basis; if the intensity is (0, 0), it is marked as the 0 basis; Bob uses the same method to set the basis of the data pair. After the basis setting is completed, Alice and Bob announce the basis of each data pair. If both announce the X basis or the Z basis, it is retained, otherwise it is discarded.

7. The quantum key distribution method based on pattern matching and passive decoy states according to claim 6, characterized in that: In S6, for each Z - basis data pair with index values of i and j , if Alice's strength ( , ) = (0, μ ), then Alice sets her key to 0, otherwise sets to 1; Bob's initial key - bit setting is exactly the opposite of Alice's, that is, Bob's strength ( , ) = (0, μ ), sets his key to 1, otherwise sets to 0; For the X-based data pair, the initial key is obtained from the relative phase, and the calculation formula is: ； Bob determines the initial key bit in a similar manner k b and the alignment angle θ b , but Bob has an additional key flipping operation: if in two rounds, the detector responses for the i and the j are (L,L) or (R,R), then Bob keeps his key bit; if the detector responses are (L,R) or (R,L), then Bob flips the key bit, and in the X basis, only when the alignment angles of Alice and Bob are equal, i.e., θ a = θ b , will the data pair be kept, otherwise the data pair will be discarded.

8. The quantum key distribution method based on pattern matching and passive decoy states according to claim 7, wherein: In S7, Alice and Bob perform parameter estimation on the phase flip error rate and qubit error rate of the Z basis.

9. The quantum key distribution method based on pattern matching and passive decoy states according to claim 8, wherein: In S8, Alice and Bob use the Z-basis pairs in the case of the transmitted signal states to generate a key, and at the same time, according to , and carry out key negotiation and privacy amplification to obtain a secure key; The expression formula of the key generation rate is: Among them, , representing the expected value of the number of pairs generated per round, l is the maximum pairing interval, p is the probability that a certain round is a successful detection event, r s is the probability that a successful detection pulse pair is a signal pair, and are respectively the expected single-photon pair example and the phase error rate of single-photon pairs in the signal pair, f is the error correction efficiency, is the bit error rate of the signal pair, is the binary Shannon entropy function.

10. A quantum key distribution system based on pattern matching and passive decoy states, characterized in that: Including two communication devices and a measurement device for performing the quantum key distribution method based on pattern pairing and passive decoy states as described in any one of claims 1 to 9, the measurement device is respectively communicatively connected to the two communication devices, and the two communication devices are communicatively connected to each other.

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