A method and system for demonstrating security of quantum key distribution

Abstract

The application discloses a system for demonstrating quantum key distribution security, which comprises a sending end, an eavesdropping end, a receiving end and a control end, wherein the control end comprises a man-machine interface module, a fourth control module, a post-processing module and a demonstration module; the man-machine interface module is used for realizing the interaction between the device and visitors; the control end sends parameter configuration instructions and acquires parameter information, key information and synchronization information through the fourth control module; the post-processing module is arranged to calculate the key consistency coefficient of the eavesdropping end key and the sending end-receiving end key after acquiring the key information and the synchronization information of the sending end, the eavesdropping end and the receiving end; and the demonstration module is used for presenting the key consistency coefficient, the sending end-receiving end code rate, the error code rate and the eavesdropping key code rate of the eavesdropping end. Through the method, the information leakage caused by the eavesdropping behavior can be effectively demonstrated from the key level.

Description

Technical Field

[0001] This invention relates to the field of quantum communication, and more specifically to a method and system for demonstrating the security of quantum key distribution. Background Technology

[0002] Quantum key distribution (QKD) is a technology that utilizes the indivisible, non-clonal, and non-measurable physical properties of photons to distribute keys and thus ensure communication security. Existing technologies have provided several devices and methods to demonstrate the security of quantum key distribution systems, helping people to more intuitively understand the practical security of quantum key distribution technology.

[0003] For example, patent application CN110247755A provides an attack demonstration device and method. A synchronous wavelength division multiplexing (SDM) module can demultiplex the photoelectric signal input to the first optoelectronic system into synchronous light and signal light, thus separating the synchronous light and signal light. A front-end interception and detection module detects the synchronous light and signal light input to the SDM module respectively. Based on the detection results of the front-end interception and detection module, a back-end retransmission light source module retransmits the corresponding back-end light source to the second optoelectronic system, or directly retransmits a preset back-end light source to the second optoelectronic system according to preset calibration feedback parameters. This attack demonstration device showcases the inherent unassailable nature of the quantum key distribution system, and an optical switch switches between attack and normal modes.

[0004] Patent CN114614978A provides a demonstration system's workflow and functional structure. By pre-setting open optical interfaces in the transmitting, receiving, and attacking ends, it allows for the configuration of the optical structure of each module and the design of the control end as needed. This demonstration system allows participants to select the attack type to be demonstrated and can automatically execute the normal quantum communication process and the quantum communication process under the attack mode according to the selected attack type, and demonstrate the corresponding quantum communication attack and defense effects.

[0005] CN103824487A provides a demonstration device and method for eavesdropping that can demonstrate beam splitting attacks, including an optical switch for switching operating modes, an optical beam splitter for combining or splitting light, and a synchronous detector for simulating an eavesdropper listening to information.

[0006] In existing technologies, it is common to observe whether changes in parameters such as count rate and bit error rate exceed thresholds to determine the presence of eavesdroppers and thus demonstrate system security. However, eavesdropping behavior has no effect on key distribution when changes are within the threshold range. On the other hand, the actual practice in the operation of business systems is to calculate the secure key generation rate using the GLLP formula. As long as the actual key generation rate is less than the secure key generation rate, it can be guaranteed that the key stolen by the eavesdropper is unrelated to the keys of the communicating parties. Current demonstration systems lack demonstration results at the key level. Summary of the Invention

[0007] The technical problem to be solved by this invention is how to effectively demonstrate the amount of information leakage caused by eavesdropping at the key level.

[0008] This invention solves the aforementioned technical problems through the following technical means: a system demonstrating the security of quantum key distribution, comprising a transmitter, an eavesdropping terminal, a receiver, and a control terminal; the control terminal is configured to configure parameters and process data for the transmitter, receiver, and eavesdropping terminal, and display the results; the transmitter is configured to generate and output signal light and synchronization light; the receiver is configured to receive signal light and synchronization light and perform decoding and detection; the eavesdropping terminal is configured to receive signal light and synchronization light and perform beam splitting operations, thereby stealing information.

[0009] The control terminal includes a human-machine interface module, a fourth control module, a post-processing module, and a demonstration module. The human-machine interface module is used to enable interaction between the device and visitors. The control terminal issues parameter configuration commands and obtains parameter information, key information, and synchronization information through the fourth control module. The post-processing module is configured to calculate the key consistency coefficient between the eavesdropping key and the sending-receiving key after the control terminal obtains the key information and synchronization information of the sending end, the eavesdropping end, and the receiving end. The demonstration module is used to present the key consistency coefficient, the sending-receiving end key generation rate, the bit error rate, and the eavesdropping end key generation rate.

[0010] As a further optimized technical solution, the post-processing module calculates the key consistency coefficient according to the following process:

[0011] 1) Assume the repetition frequency of quantum light is When the transmitter and receiver perform quantum key distribution, they use synchronization light for time synchronization, with the rising edge of the synchronization light signal as the starting point. The time between two synchronization signals is divided equally into different timestamps to create an interval, so that each key bit corresponds to a timestamp. When outputting the key, the timestamp information of each bit is also included.

[0012] 2) When the eavesdropping terminal is eavesdropping, it also uses the synchronization optical signal to add timestamp information to the output key bits, in the same way as 1). This process is carried out simultaneously with 1).

[0013] 3) After receiving the sender-receiver key and the eavesdropping key, the control end uses timestamp information and a correction sequence to align the sender-receiver key with the eavesdropping key in time. Then, it calculates the key consistency coefficient according to the following formula:

[0014] .

[0015] As a further optimized technical solution, in process 1), in order to eliminate the influence of synchronous optical noise, no code is formed at the timestamp 0 position.

[0016] As a further optimized technical solution, in process 1), a hierarchical synchronization mechanism is adopted, and a first-level synchronization signal is generated at regular intervals to generate a correction sequence. The rising edge of the first-level synchronization signal corresponds to the code '1' of the correction sequence, and the remaining positions correspond to the code '0'. The correction sequence is used for calibration to prevent large-scale signal misalignment. When outputting the key, the code corresponding to each bit of the correction sequence is also attached.

[0017] As a further optimized technical solution, the main workflow of the system demonstrating quantum key distribution security is as follows:

[0018] First, perform device initialization, start the control terminal and conduct authentication with the sending terminal, receiving terminal and eavesdropping terminal, establish a connection and reset all parameters;

[0019] Secondly, the operators configure the specific values ​​or ranges of change for each parameter according to the demonstration requirements and then distribute the configuration.

[0020] Next, the transmitting and receiving devices are activated to perform quantum key distribution;

[0021] The operator then decides whether to enable the eavesdropping mode based on the demonstration requirements: If the eavesdropping mode is not enabled, the eavesdropping end does not perform any operations, and the sending and receiving ends periodically upload key information, synchronization information, and code generation rate to the control end. The control end demonstration module then demonstrates this information. If the eavesdropping mode is enabled, the control end issues commands to the eavesdropping end, which performs a light splitting attack and generates an eavesdropping key. The sending, receiving, and eavesdropping ends periodically upload the generated key information, synchronization information, etc., to the control end. The control end performs post-processing based on the keys from the receiving and eavesdropping ends, calculates the key consistency coefficient, and then demonstrates the key consistency coefficient and code generation rate.

[0022] As a further optimized technical solution, the transmitting end includes: a signal light source providing quantum light, a synchronization light source providing synchronization light, a first negotiation light transceiver module for generating and detecting classical negotiation light, a multiplexing device, a first control module, a first key extraction module, a modulation module, and a first random number generator;

[0023] The multiplexing device is configured to multiplex quantum light and synchronous light, or to multiplex quantum light, synchronous light and negotiated light.

[0024] The first control module is used to receive control from the control terminal and feed back data. The fed back data includes the current parameter values ​​of the sending terminal, key information, and synchronization information.

[0025] The first key extraction module is used to perform base-splitting processing on the original data and obtain the key;

[0026] The modulation module is used to adjust information such as polarization, phase, and intensity of quantum light, and includes a decoy state modulation module.

[0027] The first random number generator is used to generate random numbers required during quantum modulation.

[0028] As a further optimized technical solution, the receiving end includes: a first wavelength division device, a first demodulation module, a first single-photon detector for detecting quantum light, a first synchronous optical detector for detecting synchronous light, a second negotiation optical transceiver module for generating and detecting classical negotiation light, a second key extraction module, and a second control module.

[0029] The first wavelength division device is configured to divide quantum light and synchronization light into wavelengths, or to divide quantum light, synchronization light and negotiated light into wavelengths.

[0030] The first demodulation module is used to demodulate the wavelength-divided quantum light to cooperate with the first single-photon detector to measure the quantum state;

[0031] The first synchronous optical detector is used to detect the wavelength-divided synchronous light;

[0032] The second key extraction module is used to perform basic processing on the original data and obtain the key;

[0033] The second control module is used to receive control from the control terminal and feed back data, including the current parameter values ​​of the receiving terminal, key information, and synchronization information.

[0034] As a further optimized technical solution, the eavesdropping terminal includes: a beam splitting module, a second wavelength division device, a second demodulation module, a third negotiated light transceiver module for generating and detecting classical negotiated light, a second single-photon detector for detecting quantum light, a second synchronous light detector for detecting synchronous light, a third control module, and a third key extraction module.

[0035] The second wavelength division device, the second single-photon detector, the second synchronous optical detector, the third negotiated optical transceiver module, the third control module, the third key extraction module, and the second demodulation module have the same functions as the corresponding modules at the receiving end;

[0036] The beam splitter module is used to distribute quantum light, synchronous light, and classical negotiated light to two or more optical fibers in a predetermined ratio.

[0037] As a further optimized technical solution, the beam splitting module is configured to have an adjustable beam splitting ratio, and an optical switch is set at the optical inlet of the eavesdropping end to select whether to activate the eavesdropping mode.

[0038] As a further optimized technical solution, the working steps of the eavesdropping terminal specifically include:

[0039] The optical signal transmitted by the transmitting end enters the eavesdropping device from port 1 of the first polarization-maintaining optical circulator, exits from port 2 of the first polarization-maintaining optical circulator, and enters port 1 of the first optical switch;

[0040] The first optical switch is used to select whether to enable the eavesdropping mode. If eavesdropping is not enabled, the optical signal is emitted from port 2 of the first optical switch, passes through the first coupler, and enters port 3 of the second polarization-maintaining optical circulator. It is then emitted from port 1 of the second polarization-maintaining optical circulator and transmitted to the receiving end. If the eavesdropping mode is enabled, the optical signal is emitted from port 3 of the first optical switch, passes through the adjustable split-ratio coupler, and part of the light is emitted to the first coupler and then enters port 3 of the second polarization-maintaining optical circulator. It is then emitted from port 1 of the second polarization-maintaining optical circulator and transmitted to the receiving end. The other part of the light is emitted to the first wavelength division multiplexer. The first wavelength division multiplexer splits the light into quantum light and non-quantum light. The quantum light enters the second demodulation module. The eavesdropping end can obtain relevant information based on whether the four single-photon detectors connected to the output port of the second demodulation module respond. The non-quantum light enters the second wavelength division multiplexer and is split into synchronization light and classical negotiation light. The synchronization light enters the synchronization light detector, and the classical negotiation light is detected by the negotiation light transceiver module.

[0041] The state of the second optical switch is set according to whether the eavesdropping mode is enabled. When the eavesdropping mode is enabled, the third coupler is used to split the negotiation light for eavesdropping. The classic negotiation light signal sent by the receiver enters from port 1 of the second polarization-maintaining optical circulator, exits from port 2 to the second optical switch and enters the third coupler. Part of the light enters the negotiation light transceiver module of the eavesdropping end and is eavesdropped. The remaining light passes through the second coupler to port 2 of the first polarization-maintaining circulator and exits from port 1 to the transmitting end.

[0042] The advantages of this invention are as follows: This invention proposes a system and method for demonstrating the security of quantum key distribution, and defines a key consistency coefficient to measure security. This method can effectively demonstrate the amount of information leakage caused by eavesdropping at the key level; it provides an interactive interface allowing participants to adjust parameters and intuitively experience the impact of different parameters on system security; finally, this method can demonstrate the proportion of key eavesdropping under a full range of parameters; and it proposes a hierarchical synchronization mechanism to increase the accuracy of key time alignment. Attached Figure Description

[0043] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A functional architecture diagram of a system demonstrating the security of quantum key distribution according to an embodiment of the present invention is shown schematically.

[0046] Figure 2 A schematic diagram illustrating the working principle of the synchronization technology of the present invention is provided.

[0047] Figure 3 This represents one implementation of an eavesdropping device embodiment;

[0048] Figure 4 These are simulation diagrams illustrating the demonstration effects of the corresponding embodiments;

[0049] Figure 5 This is a business process framework diagram of the demonstration system;

[0050] Figure 6 This represents another implementation of the eavesdropping device;

[0051] Figure 7 This diagram illustrates a system architecture where the sender and receiver communicate with each other. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify the corresponding elements does not imply that the element has any ordinal number, nor does it represent the order of one element with another element, or the order of manufacturing methods. The use of these ordinal numbers is only to enable a named element to be clearly distinguished from another element with the same name.

[0054] Please see Figure 1 As shown, this invention provides a system demonstrating the security of quantum key distribution, comprising a transmitter, an eavesdropping terminal, a receiver, and a control terminal. The control terminal is configured to configure parameters and process data for the transmitter, receiver, and eavesdropping terminal, and to display the results. The transmitter is configured to generate and output signal light and synchronization light. The receiver is configured to receive the signal light and synchronization light, and to decode and detect them. The eavesdropping terminal is configured to receive the signal light and synchronization light and to perform beam splitting operations, thereby enabling information theft.

[0055] Furthermore, the transmitting end may include: a signal light source providing quantum light, a synchronization light source providing synchronization light, a first negotiation light transceiver module for generating and detecting classical negotiation light, a multiplexing device, a first control module, a first key extraction module, a modulation module, and a first random number generator;

[0056] The multiplexing device is configured to multiplex quantum light and synchronous light, or to multiplex quantum light, synchronous light and negotiated light.

[0057] The first control module is used to receive control from the control terminal and feed back data. The fed back data includes the current parameter values ​​of the sending terminal, key information, and synchronization information.

[0058] The first key extraction module is used to perform base-splitting processing on the original data and obtain the key;

[0059] The modulation module is used to adjust information such as polarization, phase, and intensity of quantum light, and includes a decoy state modulation module.

[0060] The first random number generator is used to generate random numbers required during quantum modulation.

[0061] Optionally, the transmitting end can freely choose whether to transmit the negotiation light, signal light, and synchronization light together on the same fiber.

[0062] Furthermore, the receiving end may include: a first wavelength division device, a first demodulation module, a first single-photon detector for detecting quantum light, a first synchronization optical detector for detecting synchronization light, a second negotiation optical transceiver module for generating and detecting classical negotiation light, a second key extraction module, and a second control module;

[0063] The first wavelength division device is configured to divide quantum light and synchronization light into wavelengths, or to divide quantum light, synchronization light and negotiation light into wavelengths (corresponding to whether the transmitting end transmits negotiation light, signal light and synchronization light together on the same fiber).

[0064] The first demodulation module is used to demodulate the wavelength-divided quantum light to cooperate with the first single-photon detector to measure the quantum state;

[0065] The first synchronous photodetector is used to detect the synchrotron light after it has been split.

[0066] The second key extraction module is used to perform basic processing on the original data and obtain the key;

[0067] The second control module is used to receive control from the control terminal and feed back data, including the current parameter values ​​of the receiving terminal, key information, and synchronization information.

[0068] Optionally, a second random number generator can be added depending on whether the detection end adopts an active or passive detection method.

[0069] Furthermore, the eavesdropping terminal may include: a beam splitting module, a second wavelength division device, a second demodulation module, a third negotiated light transceiver module for generating and detecting classical negotiated light, a second single-photon detector for detecting quantum light, a second synchronous light detector for detecting synchronous light, a third control module, and a third key extraction module;

[0070] The second wavelength division device, the second single-photon detector, the second synchronous optical detector, the third negotiated optical transceiver module, the third control module, the third key extraction module, and the second demodulation module have the same functions as the corresponding modules at the receiving end;

[0071] The beam splitting module is used to distribute quantum light, synchronous light, and classical negotiated light to two or more optical fibers in a predetermined ratio;

[0072] Preferably, the beam splitting module is configured to have an adjustable beam splitting ratio;

[0073] Optionally, a light switch can be installed at the light inlet of the eavesdropping device to select whether to activate the eavesdropping mode;

[0074] Furthermore, the control terminal may include: a human-machine interface module, a fourth control module, a post-processing module, and a demonstration module;

[0075] The human-machine interface module is used to enable interaction between the device and visitors. Visitors can configure the parameters and modes of the sending end, the eavesdropping end, and the receiving end through the human-machine interface module.

[0076] The fourth control module is the interface between the control end and the sending end, the eavesdropping end and the receiving end. The control end can issue parameter configuration instructions to the latter three and obtain parameter information, key information and synchronization information through the fourth control module.

[0077] The post-processing module is configured to calculate the key consistency coefficient between the eavesdropping key and the sending-receiving key after obtaining the key information and synchronization information of the sending end, the eavesdropping end, and the receiving end at the control end.

[0078] The demonstration module is used to present key consistency, as well as the key generation rate and error rate between the sender and receiver, and the key generation rate of the eavesdropping end.

[0079] Furthermore, both the receiving end and the eavesdropping end randomly select measurement bases to measure quantum light;

[0080] Furthermore, the eavesdropping device uses a beam splitter module to eavesdrop on the classical negotiated optical signal for base communication;

[0081] Optionally, the sender and receiver, as well as the sender and the eavesdropping end, can each perform a classic negotiation process to achieve the demonstration effect.

[0082] See further Figure 2 As shown, in the post-processing module, the calculation of the key consistency coefficient follows the following process:

[0083] 1) Assume the repetition frequency of quantum light is When the transmitter and receiver perform quantum key distribution, they use synchronization light for time synchronization, with the rising edge of the synchronization light signal as the starting point. The time between two synchronization signals is divided equally into different timestamps to create an interval, so that each key bit corresponds to a timestamp. When outputting the key, the timestamp information of each bit is also included.

[0084] Preferably, to eliminate the influence of synchronization light noise, no code is formed at the timestamp 0 position;

[0085] Preferably, a hierarchical synchronization mechanism is adopted, in which a first-level synchronization signal is generated at regular intervals to generate a correction sequence. The rising edge of the first-level synchronization signal corresponds to the code '1' in the correction sequence, and the remaining positions correspond to the code '0'. The correction sequence is used for calibration to prevent large-scale signal misalignment. When outputting the key, the code corresponding to each bit of the correction sequence is also included.

[0086] 2) When the eavesdropping terminal is eavesdropping, it also uses the synchronization optical signal to add timestamp information to the output key bit, in the same way as 1), and this process is carried out simultaneously with 1);

[0087] 3) After receiving the sender-receiver key and the eavesdropping key, the control end uses timestamp information and a correction sequence to align the sender-receiver key with the eavesdropping key in time. Then, it calculates the key consistency coefficient according to the following formula:

[0088]

[0089] See Figure 5 As shown, the main workflow of this demonstration system is as follows:

[0090] First, perform device initialization, start the control terminal and conduct authentication with the sending terminal, receiving terminal and eavesdropping terminal, establish a connection and reset all parameters;

[0091] Secondly, the operators configure the specific values ​​or ranges of change for each parameter according to the demonstration requirements and then distribute the configuration.

[0092] Next, the transmitting and receiving devices are activated to perform quantum key distribution;

[0093] The operator then decides whether to enable the eavesdropping mode based on the demonstration requirements. If the eavesdropping mode is not enabled, the eavesdropping end will not perform any operations. The sending and receiving ends periodically upload key information, synchronization information, and code generation rate to the control end, and the control end demonstration module demonstrates this information.

[0094] If eavesdropping mode is enabled, the control terminal sends commands to the eavesdropping terminal, which then performs a light splitting attack and generates an eavesdropping key. The sending, receiving, and eavesdropping terminals periodically upload the generated key information, synchronization information, etc., to the control terminal. The control terminal performs post-processing based on the keys from the receiving and eavesdropping terminals, calculates the key consistency coefficient, and demonstrates information such as the key consistency coefficient and key generation rate.

[0095] Figure 3This is an example of an implementation of the eavesdropping terminal of the demonstration system of this invention. In this example, the QKD system adopts a polarization coding mode, and the eavesdropping terminal adopts a passive detection mode. In this embodiment, the transmitting end uses a modulation module to randomly modulate the quantum signal light emitted by the signal light source into different polarization states based on the random number generated by the random number generator. A multiplexing device then multiplexes the quantum signal light, the synchronization light generated by the synchronization light source, and the negotiation light generated by the negotiation light transceiver module onto a single optical fiber and transmits them to port 1 of the first polarization-maintaining circulator at the eavesdropping terminal. The signal then passes through port 1 of the second polarization-maintaining circulator to the receiving end. Upon receiving the signal, the receiving end uses a wavelength division device to divide the quantum signal light, synchronization light, and negotiation light signal. The quantum signal light is detected by a single-photon detector after demodulation, while the synchronization light and negotiation light are detected by the synchronization light detector and the negotiation light transceiver module, respectively. The classical information fed back by the receiving end is also carried by the negotiation light signal, transmitted through the same optical fiber to port 1 of the second polarization-maintaining circulator at the eavesdropping terminal, and exits from port 1 of the first polarization-maintaining circulator to reach the transmitting end.

[0096] The beam splitting module of the eavesdropping device includes a first optical switch and an adjustable beam splitting ratio coupler connected to one of the outputs of the first optical switch. The second beam splitting device includes a first beam splitter and a second beam splitter. There are four second single-photon detectors, which are respectively connected to the four optical output ports of the second demodulation module. In this embodiment, it also includes a second optical switch, a first coupler, a second coupler, and a third coupler.

[0097] The work steps are as follows:

[0098] The optical signal transmitted by the transmitting end enters the eavesdropping device from port 1 of the first polarization-maintaining optical circulator, exits from port 2 of the first polarization-maintaining optical circulator, and enters port 1 of the first optical switch.

[0099] The first optical switch is used to select whether to enable the eavesdropping mode. If eavesdropping is not enabled, the optical signal is emitted from port 2 of the first optical switch, passes through the first coupler, and enters port 3 of the second polarization-maintaining optical circulator. It is then emitted from port 1 of the second polarization-maintaining optical circulator and transmitted to the receiving end. If the eavesdropping mode is enabled, the optical signal is emitted from port 3 of the first optical switch, passes through the adjustable split-ratio coupler, and part of the light is emitted to the first coupler and then enters port 3 of the second polarization-maintaining optical circulator. It is then emitted from port 1 of the second polarization-maintaining optical circulator and transmitted to the receiving end. The other part of the light is emitted to the first wavelength division multiplexer. The first wavelength division multiplexer splits the light into quantum light and non-quantum light. The quantum light enters the second demodulation module. The eavesdropping end can obtain the corresponding information by checking whether the four single-photon detectors connected to the output port of the second demodulation module respond. The non-quantum light enters the second wavelength division multiplexer and is split into synchronization light and classical negotiation light. The synchronization light enters the synchronization light detector, and the classical negotiation light is detected by the negotiation light transceiver module.

[0100] The state of the second optical switch is set according to whether eavesdropping is enabled. When eavesdropping mode is enabled, the third coupler is used to split the negotiation light for eavesdropping. The classic negotiation light signal sent by the receiver enters from port 1 of the second polarization-maintaining optical circulator, exits from port 2 to the second optical switch and enters the third coupler. Part of the light enters the negotiation light transceiver module of the eavesdropping end and is eavesdropped. The remaining light passes through the second coupler to port 3 of the first polarization-maintaining circulator and exits from port 1 to the transmitting end.

[0101] As will be readily understood by those skilled in the art, if there is no need to select whether to enable the eavesdropping mode, and the system is always set to eavesdropping mode, then there is no need to set the first optical switch and the second optical switch. The signal sent by the transmitting end directly enters the adjustable beam splitting ratio coupler after the polarization-maintaining optical circulator. The negotiation light sent by the receiving end exits through port 3 of the second polarization-maintaining optical circulator and directly enters port 3 of the first polarization-maintaining optical circulator, thus being transmitted to the transmitting end. When the system is set to always be in eavesdropping mode, after the negotiation light sent by the receiving end exits through port 3 of the second polarization-maintaining optical circulator, part of the negotiation light enters the negotiation optical transceiver module of the eavesdropping end through the third coupler.

[0102] To demonstrate the effectiveness of this demonstration system and help those skilled in the art better understand the meaning and purpose of this invention, we will use the example of changing the intensity of quantum light at the transmitting end, and present a demonstration effect diagram with simulation calculations as the result. The specific calculation process is as follows:

[0103] The specified line attenuation between the transmitter and the optical splitter module is: The line attenuation between the beam splitter module and the single-photon detector at the receiving end is... The line attenuation between the beam splitter module and the single-photon detector at the receiving end is... ;

[0104] The beam splitting ratio of the beam splitter at the receiving end and the eavesdropping end is: .

[0105] The detection efficiencies of the single-photon detectors at the receiving end and the eavesdropping end are denoted as , respectively. The dark count rates are denoted as: The probabilities of the subsequent pulses are denoted as: ;

[0106] The bit flip error rates from the sender to the receiver and from the eavesdropper are denoted as follows: ;

[0107] The wavelength of quantum light is The repetition frequency is f, and the average number of photons per pulse is The average optical power of the laser is P.

[0108] Since the eavesdropping end randomly selects the measurement basis, it has a 50% probability of choosing the same measurement basis as the receiving end and a 50% probability of choosing a different measurement basis. First, consider the case where both parties choose the same measurement basis. When calculating the key consistency coefficient, there are actually only two possibilities regarding whether a bit flip error occurs when the bit sent by the sending end is detected by the receiving end or the eavesdropping end. All other cases are equivalent to these two cases. First, consider the first case, where there is no bit flip error:

[0109] The number of photons in a single pulse of quantum light emitted by the transmitter follows a Poisson distribution, and the probability of having k photons in a single pulse is:

[0110] ;

[0111] First, considering only the key sequence generated by quantum light, since optical attenuation and beam splitting by the beam splitter do not affect the probability distribution, the probability that the key bit generated by the receiver matches that of the transmitter is:

[0112] ;

[0113] The probability of inconsistency is:

[0114] ;

[0115] The probability that the key bits generated by the eavesdropping end match those of the sending end is:

[0116] ;

[0117] The probability of inconsistency is:

[0118] .

[0119] Secondly, considering the dark counting factor, even if neither the receiver nor the eavesdropping end detects a photon, the single-photon detector still has a certain probability of responding and generating a key. In the key sequence generated due to dark counting, the probability that the key bit generated by the receiver matches that of the transmitter is:

[0120] ;

[0121] The probability of inconsistency is:

[0122] ;

[0123] Similarly, the probability that the key bits generated by the eavesdropping end match those of the sending end is:

[0124] ;

[0125] The probability of inconsistency is:

[0126] ;

[0127] In the key sequence generated by the post-pulse, the probability that the key bit generated by the receiver matches that of the transmitter is:

[0128] ;

[0129] The probability of inconsistency is:

[0130] ;

[0131] Similarly, the probability that the key bits generated by the eavesdropping end match those of the sending end is:

[0132] ;

[0133] The probability of inconsistency is:

[0134] .

[0135] Therefore, the key consistency coefficient in this case is defined as follows:

[0136] ;

[0137] Next, consider another scenario: the receiving end's bits are not flipped, but the eavesdropping end's bits are flipped. It's easy to see that the key consistency coefficient is:

[0138] ;

[0139] Next, consider the case where the eavesdropping end and the receiving end choose different measurement bases. Again, we first consider the case where neither the receiving end nor the eavesdropping end flips any bits. In this case, the variables are updated as follows:

[0140] ;

[0141] ;

[0142] ;

[0143] ;

[0144] ;

[0145] ;

[0146] ;

[0147] ;

[0148] ;

[0149] It's easy to see that when a bit flip occurs between the receiving end and the eavesdropping end, it's equivalent to the situation described above, and the key consistency coefficient at this time can be calculated as follows:

[0150] ;

[0151] By using the probability of each scenario as a weight, a weighted average can be calculated to obtain the final overall key consistency coefficient:

[0152] The average number of photons per pulse is easy to know. The conversion relationship between light intensity and average light intensity P is as follows:

[0153] ;

[0154] The consistency coefficient can then be plotted. The relationship between the variable parameter P and the parameter P is illustrated in the following diagram. Figure 4 As shown, the horizontal axis represents the light intensity of the light source at the transmitting end, and the vertical axis represents the key consistency coefficient (the key consistency coefficient in the actual demonstration system is the measured value).

[0155] This method can demonstrate the impact of different parameter values ​​on security, rather than just whether eavesdropping can be detected, helping visitors to more intuitively understand the security of quantum communication systems and the importance of each parameter.

[0156] Alternatively, the eavesdropping device can also employ an active detection method, using a second random number generator to demodulate the quantum state, as shown in Example 2, referring to... Figure 6 The main difference from the example above is that the EPC in the second demodulation module randomly determines the rotation polarization angle based on the random number generated by the second random number generator.

[0157] Optionally, in some existing QKD technologies, the sender and receiver do not negotiate with each other, but instead send negotiation signals to the key manager (KM) respectively, which then performs unified scheduling, as described above. Figure 7 At this point, the eavesdropper needs to set up eavesdropping devices on three routes: the sender-receiver route, the sender-KM route, and the receiver-KM route, and then execute a light splitting attack.

[0158] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for demonstrating the security of quantum key distribution, characterized in that: It includes a transmitter, an eavesdropping device, a receiver, and a control device. The control device is configured to configure parameters and process data for the transmitter, receiver, and eavesdropping device, and to display the results. The transmitting end is configured to generate and output signal light and synchronization light; the receiving end is configured to receive signal light and synchronization light and perform decoding and detection. The eavesdropping device is configured to receive signal light and synchronization light and perform light splitting operations to steal information. The control terminal includes a human-machine interface module, a fourth control module, a post-processing module, and a demonstration module. The human-machine interface module is used to enable interaction between the device and visitors. The control terminal issues parameter configuration commands and obtains parameter information, key information, and synchronization information through the fourth control module. The post-processing module is configured to calculate the key consistency coefficient between the eavesdropping key and the sending-receiving key after the control terminal obtains the key information and synchronization information of the sending end, the eavesdropping end, and the receiving end. The demonstration module is used to present the key consistency coefficient, the sending-receiving end code generation rate, the bit error rate, and the eavesdropping end eavesdropping key code generation rate. The key consistency coefficient is calculated following this process: 1) Assuming the quantum light repetition frequency is f, when the transmitter and receiver perform quantum key distribution, they use synchronization light for time synchronization. Taking the rising edge of the synchronization light signal as the starting point, the time between the two synchronization signals is divided equally into different timestamps with 1 / f as the interval, so that each key bit is matched with a timestamp. When the key is output, the timestamp information of each bit is also attached. 2) When the eavesdropping terminal is eavesdropping, it also uses the synchronization optical signal to add timestamp information to the output key bits, in the same way as 1); 3) After receiving the sender-receiver key and the eavesdropping key, the control end uses timestamp information and a correction sequence to align the sender-receiver key with the eavesdropping key in time. Then, it calculates the key consistency coefficient according to the following formula: 。 2. The system for demonstrating quantum key distribution security as described in claim 1, characterized in that: In process 1), in order to eliminate the influence of synchronization light noise, no code is generated at the timestamp 0 position.

3. A system for demonstrating the security of quantum key distribution as described in claim 1, characterized in that: In process 1), a hierarchical synchronization mechanism is adopted. A first-level synchronization signal is generated at regular intervals to generate a correction sequence. The rising edge of the first-level synchronization signal corresponds to the code '1' of the correction sequence, and the remaining positions correspond to the code '0'. The correction sequence is used for calibration to prevent large-scale signal misalignment. When outputting the key, the code corresponding to each bit of the correction sequence is also attached.

4. A system for demonstrating the security of quantum key distribution as described in claim 1, characterized in that: The main workflow of the system is as follows: First, perform device initialization, start the control terminal and conduct authentication with the sending terminal, receiving terminal and eavesdropping terminal, establish a connection and reset all parameters; Secondly, the operators configure the specific values ​​or ranges of change for each parameter according to the demonstration requirements and then distribute the configuration. Next, the transmitting and receiving devices are activated to perform quantum key distribution; The operator then decides whether to enable the eavesdropping mode based on the demonstration requirements: If the eavesdropping mode is not enabled, the eavesdropping end does not perform any operations, and the sending and receiving ends periodically upload key information, synchronization information, and code generation rate to the control end. The control end demonstration module then demonstrates this information. If the eavesdropping mode is enabled, the control end issues commands to the eavesdropping end, which performs a light splitting attack and generates an eavesdropping key. The sending, receiving, and eavesdropping ends periodically upload the generated key information, synchronization information, etc., to the control end. The control end performs post-processing based on the keys from the receiving and eavesdropping ends, calculates the key consistency coefficient, and then demonstrates the key consistency coefficient and code generation rate.

5. A system for demonstrating quantum key distribution security as described in claim 1, characterized in that: The transmitting end includes: a signal light source providing quantum light, a synchronization light source providing synchronization light, a first negotiation light transceiver module for generating and detecting classical negotiation light, a multiplexing device, a first control module, a first key extraction module, a modulation module, and a first random number generator; The multiplexing device is configured to multiplex quantum light and synchronous light, or to multiplex quantum light, synchronous light and negotiated light. The first control module is used to receive control from the control terminal and feed back data. The fed back data includes the current parameter values ​​of the sending terminal, key information, and synchronization information. The first key extraction module is used to perform base-splitting processing on the original data and obtain the key; The modulation module is used to adjust information such as polarization, phase, and intensity of quantum light, and includes a decoy state modulation module. The first random number generator is used to generate random numbers required during quantum modulation.

6. A system for demonstrating quantum key distribution security as described in claim 5, characterized in that: The receiving end includes: a first wavelength division device, a first demodulation module, a first single-photon detector for detecting quantum light, a first synchronous optical detector for detecting synchronous light, a second negotiation optical transceiver module for generating and detecting classical negotiation light, a second key extraction module, and a second control module. The first wavelength division device is configured to divide quantum light and synchronization light into wavelengths, or to divide quantum light, synchronization light and negotiated light into wavelengths. The first demodulation module is used to demodulate the wavelength-divided quantum light to cooperate with the first single-photon detector to measure the quantum state; The first synchronous photodetector is used to detect the synchrotron light after it has been split. The second key extraction module is used to perform basic processing on the original data and obtain the key; The second control module is used to receive control from the control terminal and feed back data, including the current parameter values ​​of the receiving terminal, key information, and synchronization information.

7. A system for demonstrating the security of quantum key distribution as described in claim 6, characterized in that: The eavesdropping terminal includes: a beam splitting module, a second wavelength division device, a second demodulation module, a third negotiated light transceiver module for generating and detecting classical negotiated light, a second single-photon detector for detecting quantum light, a second synchronous light detector for detecting synchronous light, a third control module, and a third key extraction module. The second wavelength division device, the second single-photon detector, the second synchronous optical detector, the third negotiated optical transceiver module, the third control module, the third key extraction module, and the second demodulation module have the same functions as the corresponding modules at the receiving end; The beam splitter module is used to distribute quantum light, synchronous light, and classical negotiated light to two or more optical fibers in a predetermined ratio.

8. A system for demonstrating the security of quantum key distribution as described in claim 7, characterized in that: The beam splitting module is configured to have an adjustable beam splitting ratio, and an optical switch is installed at the optical inlet of the eavesdropping end to select whether to activate the eavesdropping mode.

9. A system for demonstrating quantum key distribution security as described in claim 8, characterized in that: The specific operational steps of the eavesdropping device include: The optical signal transmitted by the transmitting end enters the eavesdropping device from port 1 of the first polarization-maintaining optical circulator, exits from port 2 of the first polarization-maintaining optical circulator, and enters port 1 of the first optical switch; The first optical switch is used to select whether to enable the eavesdropping mode. If eavesdropping is not enabled, the optical signal is emitted from port 2 of the first optical switch, passes through the first coupler, and enters port 3 of the second polarization-maintaining optical circulator. It is then emitted from port 1 of the second polarization-maintaining optical circulator and transmitted to the receiving end. If the eavesdropping mode is enabled, the optical signal is emitted from port 3 of the first optical switch, passes through the adjustable split-ratio coupler, and part of the light is emitted to the first coupler and then enters port 3 of the second polarization-maintaining optical circulator. It is then emitted from port 1 of the second polarization-maintaining optical circulator and transmitted to the receiving end. The other part of the light is emitted to the first wavelength division multiplexer. The first wavelength division multiplexer splits the light into quantum light and non-quantum light. The quantum light enters the second demodulation module. The eavesdropping end can obtain relevant information based on whether the four single-photon detectors connected to the output port of the second demodulation module respond. The non-quantum light enters the second wavelength division multiplexer and is split into synchronization light and classical negotiation light. The synchronization light enters the synchronization light detector, and the classical negotiation light is detected by the negotiation light transceiver module. The state of the second optical switch is set according to whether the eavesdropping mode is enabled. When the eavesdropping mode is enabled, the third coupler is used to split the negotiation light for eavesdropping. The classic negotiation light signal sent by the receiver enters from port 1 of the second polarization-maintaining optical circulator, exits from port 2 to the second optical switch and enters the third coupler. Part of the light enters the negotiation light transceiver module of the eavesdropping end and is eavesdropped. The remaining light passes through the second coupler to port 2 of the first polarization-maintaining circulator and exits from port 1 to the transmitting end.

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