A method and apparatus for detecting the actual security of measurement-device-independent quantum key distribution systems.
By introducing a legitimate optical input port and a frequency-locking controller into the quantum key distribution system, adjusting the consistency of optical wavelength, and using a detection device to detect optical power, the problem of reference light damaging the security key is solved, and security detection of measurement-device-independent systems is realized, thereby improving the system's security and detection accuracy.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NAT UNIV OF DEFENSE TECH
- Filing Date
- 2024-10-23
- Publication Date
- 2026-07-17
Smart Images
Figure CN119382875B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of quantum secure communication technology, and specifically relates to a method and apparatus for detecting the actual security of a measurement device-independent quantum key distribution system. Background Technology
[0002] Quantum key distribution (QKD) is a key distribution technique that follows the fundamental laws of quantum mechanics. It has been theoretically demonstrated that this technique can provide secure and consistent keys for Alice and Bob, who live remotely.
[0003] Over the past three decades, QKD technology has rapidly developed and matured, enabling practical deployment in commercial fiber optic networks. In QKD systems, photons are the carriers of quantum keys, most of which are scattered and absorbed during transmission. Unlike traditional optical communication, quantum signals cannot be amplified, resulting in a very low detection probability for the receiver, hindering long-distance QKD deployment. Therefore, achieving long-distance QKD has been a major research focus. Fortunately, the advent of measurement-device-independent quantum key distribution systems has not only set record after record in transmission distance but also significantly improved security compared to traditional point-to-point QKD protocols. It is noteworthy that a key component plays a crucial role in these experiments that continuously push the limits of transmission distance: optical frequency locking. The optical frequency locking component requires the assistance of a reference light to ensure wavelength consistency between Alice and Bob. Therefore, the standard approach is to place the reference light under Charlie's control, as this light is typically classical, untrusted, and does not participate in the final encoding. Charlie uses an ultra-stable laser to prepare the reference light and transmits it to Alice and Bob. After receiving the reference light, Alice and Bob first perform a beat frequency measurement between their light and the reference light. Then, they use a piezoelectric transducer (PZT) to adjust the wavelength of the laser source. When the adjustment efficiency cannot match the changes in the reference light, an acousto-optic modulator (AOM) is used for rapid adjustment. It's easy to see that since the reference light is input from the outside into Alice and Bob's system, this could compromise the actual security of the security key.
[0004] To verify the impact of this structure on the actual security of the key distribution system, we propose a method and apparatus for detecting the actual security of a measurement device-independent quantum key distribution system.
[0005] CN2022114134805, "Vulnerability Detection Device and Method for Optical Power Limiter in Quantum Secure Communication System," and CN2021105983199, "A Synchronization Correction Vulnerability Detection Method and Device in Quantum Key Distribution System," are prior works of the inventors' team, but they still belong to standard methods, which place the reference light under Charlie's control. Summary of the Invention
[0006] The purpose of this invention is to provide a method and apparatus for detecting the actual security of measurement-device-independent quantum key distribution systems. In existing technologies, Alice and Bob add a legal input port to receive reference light to ensure wavelength consistency, a feature absent in previous point-to-point QKD protocols. Furthermore, research on acousto-optic modulators reveals that the light loss caused by these modulators is not fixed but varies with frequency modulation. This uncertainty could ultimately render the secure key insecure.
[0007] The technical solution of this invention addresses the detection method and apparatus for the security of quantum key distribution systems, particularly for the detection method and apparatus for the actual security of measurement-device-independent quantum key distribution systems. It is based on the following device: In measurement-device-independent continuous-variable quantum secure communication, the quantum light source is changed from a single preparation party to two parties, namely Alice and Bob, and the quantum measurement end changes from the trusted end Bob to the untrusted third party Charlie. This structural adjustment gives quantum secure communication the ability to be immune to attacks targeting the probe end, but also places higher demands on the quantum light source, namely, the consistency of light wavelength. Therefore, in addition to using an ultrastable laser to generate photon light sources, Alice and Bob also need a reference light as a benchmark to ensure the consistency of their light wavelengths. It should be noted that this reference light does not participate in the quantum key encoding process and is defined as an untrusted light source. Therefore, a common approach is to place the laser source of this reference light at the untrusted third party Charlie. Charlie prepares the reference light and sends it to Alice and Bob simultaneously. Alice and Bob compare the difference between their own laser light source and the reference light using a frequency-locking controller, and respectively send adjustment information to their own laser and the first or third acousto-optic modulator. However, since the reference light is input from the outside into Alice and Bob's interior, this could compromise the actual security of the secure key. To verify the impact of this structure on the actual security of the key distribution system, we propose a method and apparatus for detecting the actual security of a measurement-device-independent quantum key distribution system. Figure 1 As shown, its working mode is as follows:
[0008] A) Charlie uses a second laser to produce a reference beam, which is then sent to Alice and Bob;
[0009] B) The detection device adds a second acousto-optic modulator to the open propagation path of the reference light and controls the second acousto-optic modulator to change the wavelength of the reference light through a frequency hopping controller;
[0010] C) The reference light enters Alice's first frequency-locking controller and Bob's second frequency-locking controller through the legal optical inlet;
[0011] D) Alice identifies the difference between the signal light of the first laser and the reference light by using beat frequency, and then sends adjustment information to the first laser and the first acousto-optic modulator based on the difference information, so that its own laser output laser frequency is consistent with the frequency of the reference light or a fixed difference.
[0012] E) Bob identifies the difference between the signal light of the third laser and the reference light by using beat frequency, and then sends adjustment information to the third laser and the third acousto-optic modulator based on the difference information, so that the laser output frequency of his own laser is consistent with the frequency of the reference light or a fixed difference.
[0013] F) The detection device detects the optical power of the signal output by Alice in a public quantum channel. If the optical power is greater than the rated value, it indicates that there is a design flaw in the actual security of the measured subkey distribution system.
[0014] G) The detection device detects the signal optical power output by Bob in the public quantum signal. If the optical power is greater than the rated value, it indicates that there is a design flaw in the actual security of the measured subkey distribution system.
[0015] The above A), B), C), D), E), F), and G) are carried out during the operation of the quantum secure communication system.
[0016] In A), the second laser is an ultrastable laser; in B), the adjustable range of the second acousto-optic modulator should be less than or equal to the adjustable range of the first acousto-optic modulator; in C), the legitimate input port refers to the input port actively opened by Alice and Bob to receive the reference light; in D), the signal light of the first laser refers to the light pulse used by Alice to load encoded information during quantum key distribution; in E), the signal light of the third laser refers to the light pulse used by Bob to load encoded information during quantum key distribution; in F), detecting the signal light power output by Alice in the public quantum signal detection means that the detection device places a third beam splitter on the public quantum channel from Alice to Charlie, splitting Alice's quantum light into two, sending one part to Charlie, and performing optical power detection on the other part; in G), detecting the signal light power output by Bob in the public quantum signal detection means that the detection device places a fourth beam splitter on the public quantum channel from Bob to Charlie, splitting Bob's quantum light into two, sending one part to Charlie, and performing optical power detection on the other part.
[0017] Specific methods are as follows Figure 1 As shown, its working mode is as follows:
[0018] A) Charlie uses a second laser, an ultra-stable laser, to output standard wavelength light, which is then sent to Alice and Bob;
[0019] B) The detection device adds a second acousto-optic modulator to the open propagation path of the reference light, and controls the second acousto-optic modulator to change the wavelength of the reference light through a frequency hopping controller. The adjustable range of the second acousto-optic modulator should be less than or equal to the adjustable range of the first acousto-optic modulator.
[0020] C) The reference light enters the frequency-locked controller through the input port actively opened by Alice and Bob for receiving the reference light;
[0021] D) Alice identifies the difference between the signal light and the reference light of the first laser by beat frequency, and then sends adjustment information to the first laser and the first acousto-optic modulator based on the difference information. The signal light refers to the optical pulse that Alice uses to carry encoded information.
[0022] E) Bob identifies the difference between the signal light and the reference light of the third laser by using beat frequency, and then sends adjustment information to the third laser and the third acousto-optic modulator based on the difference information. The signal light refers to the optical pulse that Bob uses to carry encoded information.
[0023] F) The detection device places a third beam splitter on the public quantum channel from Alice to Charlie; it splits Alice's quantum light in two, sending one part to Charlie and using the other part for optical power detection. If the optical power is greater than the design value, it indicates that the actual security of the measured subkey distribution system has a design flaw.
[0024] G) The detection device places a fourth beam splitter on the public quantum channel from Bob to Charlie; it splits Bob's quantum light in two, sending one part to Charlie and using the other part for optical power detection. If the optical power is greater than the design value, it indicates that the actual security of the measured quantum key distribution system has a design flaw. Attached Figure Description
[0025] Figure 1 This is a detection diagram for a measurement device-independent quantum key distribution system.
[0026] Figure 2 The attenuation of signal light by an acousto-optic modulator varies at different frequencies.
[0027] Figure 3 The impact on the secure key rate of QKD when design flaws exist. Detailed Implementation
[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0029] Figure 1 The description includes Alice, Bob, the detection device, and the Charlie unit: The first laser in the Alice unit generates the initial laser beam, which connects to the first beam splitter. One beam is used for subsequent series connection of the first acousto-optic modulator, the first phase modulator, and the first polarization modulator; the other beam is used for reference or control, etc. The first acousto-optic modulator modulates the optical signal. The first phase modulator changes the phase of the light; the first polarization modulator changes the polarization state of the light, which passes through the first attenuator and is then connected to the input of the third beam splitter; the first frequency-locked controller is connected to the first acousto-optic modulator. The third laser in the Bob unit generates another laser beam to provide a light source for Bob's end. It is connected to the fifth beam splitter, which splits the laser beam. One beam is connected to a series of three modulators: a third acousto-optic modulator, a second phase modulator, and a second polarization modulator. After passing through a second attenuator, it is connected to the input of the fourth beam splitter. The second frequency-locking controller is connected to the third acousto-optic modulator. The detection device and Charlie unit include the third and fourth beam splitters: they send the optical signals from Alice and Bob to the first and second power detectors, respectively, to detect the power of the optical signals. A second laser is provided and connected to the second acousto-optic modulator and the second beam splitter. The second beam splitter splits the laser beam into two paths, which are connected to the first and second frequency-locking controllers, respectively. A frequency-hopping controller is also provided and connected to the control terminal of the second acousto-optic modulator. The outputs of the third and fourth beam splitters are connected to the measurement port. The above steps are performed in a quantum secure communication system.
[0030] The first beam splitter has a beam ratio of 50:50; the second beam splitter has a beam ratio of 50:50; the third beam splitter has a beam ratio of 50:50; the fourth beam splitter has a beam ratio of 50:50; and the fifth beam splitter has a beam ratio of 50:50.
[0031] Example 1
[0032] This invention discloses a method and apparatus for detecting the actual security of a measurement-device-independent quantum key distribution system. The detection apparatus modulates the wavelength of a reference light emitted by Charlie using a second acousto-optic modulator and sends it to Alice and Bob. Upon receiving the reference light, Alice and Bob's frequency-locking controllers issue a frequency modulation command to a first acousto-optic modulator, causing an unexpected change in the signal light loss of the first acousto-optic modulator. This unexpected change results in the optical power of the signal light emitted by Alice and Bob exceeding a set value, thus posing a risk to the secure key.
[0033] The implementation steps are as follows:
[0034] Step A1: The detection device outputs electrical signals of quantum repetition frequencies via a frequency hopping controller, namely f1 and f2 = f1 + f2. Δ The electrical signal controls the production of two alternating wavelength reference optical signals via a second acousto-optic modulation, where the alternation repetition frequency is f. λ .
[0035] In step A2, the frequency-locking controllers of Alice and Bob units obtain two alternating beat frequency values by beating the reference light and their own laser beam. This results in the first acousto-optic modulator emitting a repetition frequency f. λ Two electrical signals cause the first acousto-optic modulator to continuously change Alice's laser wavelength and the third acousto-optic modulator to continuously change Bob's laser wavelength.
[0036] In step A3, the detection device measures half of the optical signal emitted by Alice using a third optical beam splitter to obtain the optical power value P. A .
[0037] In step A5, the detection device measures half of the optical signal emitted by Bob using the fourth optical beam splitter to obtain the optical power value P. b .
[0038] Step A6, if P is measured A or P B If any value exceeds the design value (the design value is provided by the quantum key distribution system being tested; generally, the average number of photons in the output light intensity of the quantum key distribution system is <1), it indicates that the actual security of the quantum key distribution system being tested has a design flaw.
[0039] Figure 3 The detection device performed a safety simulation model of the system under test to evaluate the actual safety of the system, categorizing it into three different scenarios: the detection device detected no design flaws in the system under test, a design flaw exists but the system is unaware of it, and a flaw exists but the system is aware of it. Here, g represents the gain value of the optical power obtained by the detection device through detecting the optical power value.
[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.
Claims
1. A method for detecting the security of a quantum key distribution system, characterized in that, Based on the quantum key distribution system, the quantum light source is prepared by two parties, namely Alice and Bob, and the quantum measurement end is changed from the trusted Bob to the untrusted third party Charlie. The first laser in Alice generates the initial laser beam, which is then connected to the first beam splitter. One beam is used for the subsequent cascaded first acousto-optic modulator, first phase modulator, and first polarization modulator; the other beam is used for reference or control. The first acousto-optic modulator modulates the optical signal. The first phase modulator changes the phase of the light; the first polarization modulator changes the polarization state of the light. After passing through the first attenuator, the light is connected to the input of the third beam splitter. The first frequency-locking controller is connected to the first acousto-optic modulator. The third laser in Bob generates another laser beam to provide a light source for Bob's end. This beam is connected to the fifth beam splitter, which splits the laser beam. One beam is connected to the third acousto-optic modulator, the second phase modulator, and the second polarization modulator in series. After passing through the second attenuator, it is connected to the input of the fourth beam splitter. The second frequency-locking controller is connected to the third acousto-optic modulator. The detection device and Charlie unit include a third beam splitter and a fourth beam splitter: these send the optical signals from Alice and Bob to the first power detector and the second power detector, respectively, to detect the power of the optical signals. A second laser is provided and connected to the second acousto-optic modulator and the second beam splitter. The second beam splitter splits the light into two paths, which are connected to the first and second frequency-locking controllers, respectively. A frequency-hopping controller is also provided and connected to the control terminal of the second acousto-optic modulator. The outputs of the third and fourth beam splitters are connected to the measurement port. Alice and Bob use an ultrastable laser to generate a photon source and require a reference light as a benchmark. This reference light does not participate in the quantum key encoding process and is defined as an untrusted source. The laser source of this reference light is placed in an untrusted third party, Charlie. Charlie prepares the reference light and sends it to Alice and Bob. Alice and Bob compare the difference between their own laser source and the reference light using a frequency-locking controller and send adjustment information to their own laser and acousto-optic modulator. The working mode of the detection method and device for the actual security of the quantum key distribution system is as follows: A) Charlie uses a second laser to produce a reference beam, which is then sent to Alice and Bob; B) The detection device adds a second acousto-optic modulator to the open propagation path of the reference light and controls the second acousto-optic modulator to change the wavelength of the reference light through a frequency hopping controller; C) The reference light enters Alice's first frequency-locking controller and Bob's second frequency-locking controller through the legal optical inlet; D) Alice identifies the difference between the signal light of the first laser and the reference light by using beat frequency, and then sends adjustment information to the first laser and the first acousto-optic modulator based on the difference information; E) Bob identifies the difference between the signal light of the third laser and the reference light by using beat frequency, and then sends adjustment information to the third laser and the third acousto-optic modulator based on the difference information. F) The detection device detects the optical power of the signal output by Alice in the public quantum signal. If the optical power is greater than the design value, it indicates that there is a design flaw in the actual security of the measured subkey distribution system. G) The detection device detects the optical power of the signal output by Bob in the public quantum signal. If the optical power is greater than the design value, it indicates that there is a design flaw in the actual security of the measured quantum key distribution system. In F) above, the signal optical power output by Alice in the public quantum signal detection refers to the detection device placing a third beam splitter on the public quantum channel from Alice to Charlie; splitting Alice's quantum light into two, sending one part to Charlie, and connecting the other part to the measurement port for optical power detection; In G) above, the signal optical power of Bob's output in the publicly disclosed quantum signal detection refers to the detection device placing a fourth beam splitter on the publicly disclosed quantum channel from Bob to Charlie; splitting Bob's quantum light into two, sending one part to Charlie, and connecting the other part to the measurement port for optical power detection.
2. The method according to claim 1, characterized in that, The above A), B), C), D), E), F), and G) are carried out during the operation of the quantum secure communication system.
3. The method according to claim 1, characterized in that, The second laser in A) above is an ultra-stable laser.
4. The method according to claim 1, characterized in that, In B) above, the adjustable range of the second acousto-optic modulator should be less than or equal to the adjustable range of the first acousto-optic modulator.
5. The method according to claim 1, characterized in that, The legitimate optical input port in C) above refers to the optical input port that Alice and Bob actively open to receive the reference light.
6. The method according to claim 1, characterized in that, In the above D), the signal light of the first laser refers to the light pulse that Alice uses to load encoded information during the quantum key distribution process.
7. The method according to claim 1, characterized in that, In E) above, the signal light of the third laser refers to the light pulse that Bob uses to load encoded information during the quantum key distribution process.