Method and device for detecting actual safety of quantum key distribution system irrelevant to measurement equipment

Abstract

The invention discloses a method and device for detecting the actual safety of a quantum key distribution system irrelevant to measurement equipment, based on the quantum key distribution system, quantum light sources are two preparation parties, namely Alice and Bob, and a quantum measurement end is changed from a trusted end Bob to an untrusted third-party Charlie; alice and Bob use an ultra-stable laser to generate a photon light source and need a reference light as a benchmark; the method comprises the following steps: A) testing equipment changes the optical wavelength of reference light in a public channel; b) the reference light enters a frequency locking controller of a sending end; c) the frequency locking controller of the transmitting end sends an adjusting instruction to the acousto-optic modulator and the laser of the transmitting end by taking the reference light as a benchmark, so that the wavelength of the output light is consistent with the wavelength of the reference light; and D) the test equipment detects the optical power of the sending end, and if the optical power is greater than a design value, the actual safety has design defects.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum secure communication, and in particular relates to a method and device for detecting the actual security of a quantum key distribution system that is independent of measurement equipment. Background Art

[0002] Quantum key distribution (QKD) is a key distribution technology that follows the basic laws of quantum mechanics. It has been theoretically demonstrated that this technology can provide secure and consistent keys for remote Alice and Bob.

[0003] In the past three decades, QKD technology has developed rapidly and matured to be deployed in commercial fiber optic networks. In QKD systems, photons are the carriers of quantum keys, most of which are scattered and absorbed in the transmission channel. Unlike traditional optical communications, quantum signals cannot be amplified, resulting in a very low probability of detection at the receiver, which hinders the long-distance deployment of QKD. Therefore, achieving long-distance QKD has always been a major research focus. Fortunately, the birth of the measurement device-independent quantum key distribution system has not only created one record after another in terms of transmission distance, but also has greatly improved security compared to traditional point-to-point QKD protocols. It should be noted that in the experiments that continuously break the limit of transmission distance, a key component plays a vital role, called optical frequency locking. The optical frequency locking component requires the assistance of reference light to ensure the wavelength consistency of Alice and Bob. Therefore, the standard method is to put the reference light under Charlie's control, because this light is usually classical, untrusted, and does not participate in the final encoding. Charlie uses an ultra-stable laser to prepare the reference light and transmit it to Alice and Bob. After Alice and Bob receive the reference light, they 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 change of the reference light, an acousto-optic modulator (AOM) is used for fast adjustment. It is not difficult to see that since the reference light is input from the outside to the inside of Alice and Bob, this may damage the actual security of the security key.

[0004] In order to verify the impact of this structure on the actual security of the key distribution system, we propose a detection method and device for the actual security of a quantum key distribution system that is independent of the measurement device.

[0005] CN2022114134805 A vulnerability detection device and method for an optical power limiter in a quantum secure communication system, CN2021105983199 A method and device for synchronously correcting vulnerability detection in a quantum key distribution system are prior work by the inventor's team, but they are still standard methods, which put the reference light under the control of Charlie. Summary of the invention

[0006] The purpose of the present invention is to provide a method and device for detecting the actual security of a quantum key distribution system that is independent of the measurement device. In the prior art, in order to ensure that the wavelengths of light are consistent with each other, Alice and Bob added a legal light input port for receiving reference light, which did not exist in the previous point-to-point QKD protocol. In addition, through the study of the acousto-optic modulator, it was found that the loss of light caused by the acousto-optic modulator is not a fixed value, but changes with the change of frequency modulation. This uncertainty is likely to eventually cause the security key to become unsafe.

[0007] The technical solution of the present invention is a detection method and device for the security of a quantum key distribution system, especially a detection method and device for the actual security of a quantum key distribution system that is independent of a measurement device, based on the following device: in the process of continuous variable quantum secure communication that is independent of the measurement device, the quantum light source is changed from the original single preparation party to two preparation parties, namely Alice and Bob, and the quantum measurement end is changed from the trusted end Bob to the untrusted third party Charlie. The structural adjustment gives quantum secure communication the ability to be immune to attacks on the detection end, and also puts forward higher requirements on the quantum light source, namely the consistency of the light wavelength. Therefore, in addition to using an ultra-stable laser to generate a photon light source, Alice and Bob also need a reference light as a reference to ensure that the wavelengths of each other's light are consistent. It should be noted that the reference light does not participate in the encoding process of the quantum key and is defined as an untrusted light source. Therefore, a more common way is to place the laser source of the reference light in the untrusted third party Charlie. Charlie prepares the reference light and sends it to Alice and Bob at the same time. Alice and Bob compare the difference between their own laser light source and the reference light through a frequency locking controller, and send adjustment information to their own laser and the first or third acousto-optic modulator respectively. However, since the reference light is input from the outside to the inside of Alice and Bob, this may damage the actual security of the security key. In order to verify the impact of this structure on the actual security of the key distribution system, we propose a detection method and device for the actual security of the quantum key distribution system that is independent of the measurement device. Figure 1 As shown, its working mode is as follows:

[0008] A) Charlie uses a second laser to produce reference light, which he then sends to Alice and Bob.

[0009] B) the detection device adds a second acousto-optic modulator to the public 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 light input port;

[0011] D) Alice identifies the difference between the signal light of the first laser and the reference light by means of beat frequency, and then sends adjustment information to the first laser and the first acousto-optic modulator according to the difference information, so that the laser frequency output by its own laser 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 means of beat frequency, and then sends adjustment information to the third laser and the third acousto-optic modulator according to the difference information, so that the laser frequency of its own laser output 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 the public quantum channel. If the optical power is greater than the rated value, it means that there is a design flaw in the actual security of the measured sub-key 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 means that there is a design flaw in the actual security of the measured sub-key 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] The second laser in A) is an ultra-stable laser; the adjustable range of the second acousto-optic modulator in B) should be less than or equal to the adjustable range of the first acousto-optic modulator; the legal light input port in C) refers to the light input port that Alice and Bob actively open to receive reference light; the signal light of the first laser in D) refers to the light pulse used by Alice to carry coded information during quantum key distribution; the signal light of the third laser in E) refers to the light pulse used by Bob to carry coded information during quantum key distribution; the signal light power output by Alice in the public quantum signal detection in F) refers to that the detection device places a fifth beam splitter on the public quantum channel from Alice to Charlie; divides Alice's quantum light into two, sends one part to Charlie, and performs optical power detection on the other part; the signal light power output by Bob in the public quantum signal detection in G) refers to that the detection device places a fourth beam splitter on the public quantum channel from Bob to Charlie; divides Bob's quantum light into two, sends one part to Charlie, and performs optical power detection on the other part.

[0017] Specific methods such as Figure 1 As shown, its working mode is as follows:

[0018] A) Charlie uses the second laser as 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 AOM to the public propagation path of the reference light, and controls the second AOM to change the wavelength of the reference light through a frequency hopping controller. The adjustable range of the second AOM should be less than or equal to the adjustable range of the first AOM;

[0020] C) The reference light enters the frequency locking controller through the light inlet that Alice and Bob actively open to receive the reference light;

[0021] D) Alice identifies the difference between the signal light of the first laser and the reference light by means of beat frequency, and then sends adjustment information to the first laser and the first acousto-optic modulator according to the difference information. The signal light refers to the optical pulse used by Alice to carry the coded information;

[0022] E) Bob identifies the difference between the signal light of the third laser and the reference light by means of beat frequency, and then sends adjustment information to the third laser and the third acousto-optic modulator according to the difference information. The signal light refers to the optical pulse used by Bob to carry the coded information;

[0023] F) The detection device places a fifth beam splitter on the public quantum channel from Alice to Charlie; it splits Alice's quantum light into two, one part is sent to Charlie, and the other part is used for optical power detection. If the optical power is greater than the design value, it means that there is a design flaw in the actual security of the measured subkey distribution system;

[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 into two, one part is sent to Charlie, and the other part is used for optical power detection. If the optical power is greater than the design value, it means that there is a design flaw in the actual security of the measured sub-key distribution system.

[0025] F) The beam splitting ratio of the first beam splitter is 50:50; the beam splitting ratio of the second beam splitter is 50:50; the beam splitting ratio of the third beam splitter is 50:50; the beam splitting ratio of the fourth beam splitter is 50:50; and the beam splitting ratio of the fifth beam splitter is 50:50.

[0026] Connection method reference Figure 1 BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Detection diagram for the measurement device-independent quantum key distribution system.

[0028] Figure 2The attenuation of the signal light by the acousto-optic modulator changes when it operates at different frequencies.

[0029] Figure 3 Impact on the secure key rate of QKD when design flaws exist. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] The embodiment of the present invention provides a detection method and device for the actual security of a quantum key distribution system that is independent of measurement equipment. The detection device changes the wavelength of the reference light emitted by Charlie through a second acousto-optic modulator and sends it to Alice and Bob. After receiving the reference light, the frequency locking controllers of Alice and Bob send a frequency modulation instruction to the first acousto-optic modulator, resulting in an unexpected change in the loss of the signal light by the first acousto-optic modulator. The unexpected change causes the optical power of the signal light emitted by Alice and Bob to be greater than the set value, thereby bringing risks to the security key.

[0033] The implementation steps are as follows:

[0034] Step A1: The detection device outputs the electrical signal of quantum repetition frequency through the frequency hopping controller, which are f1 and f2 = f1 + f Δ The electrical signal controls the production of two reference optical signals with alternating wavelengths through the second acousto-optic modulation, where the alternating repetition frequency is f λ .

[0035] Step A2: Alice and Bob's frequency-locked controllers beat the reference light with their own lasers to obtain two alternating beat frequency values. Thus, the first AOM emits a repetition frequency of f λ The two electrical signals cause the first acousto-optic modulator to continuously change the laser wavelengths of Alice and Bob.

[0036] Step A3: The detection device measures half of the optical signal emitted by Alice through the third optical beam splitter to obtain an optical power value P A .

[0037] Step A5: The detection device measures half of the optical signal emitted by Bob through the fourth optical beam splitter to obtain an optical power value P B .

[0038] Step A6, if the measured P A or P B If any one of them is greater than 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 means that there is a design flaw in the actual security of the quantum key distribution system being measured.

[0039] Figure 3 The detection device simulates the safety of the system under test to evaluate the actual safety of the system, which includes three different situations: the detection device detects that the system under test has no design defects, there are design defects and the system is not aware of them, and there are defects and the system is aware of them. Among them, g is the gain value of the optical power obtained by the detection device through detecting the optical power value.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope 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 end Bob to the untrusted third party Charlie; Alice and Bob use ultra-stable lasers to generate photon light sources and need a reference light as a benchmark. The reference light does not participate in the encoding process of the quantum key and is defined as an untrusted light source. The laser source of the reference light is placed in the untrusted third party Charlie; Charlie prepares the reference light and sends it to Alice and Bob at the same time; Alice and Bob compare the difference between their own laser light source and the reference light through the frequency locking controller, and send adjustment information to their own lasers and acousto-optic modulators; the actual security detection method and device working mode of the quantum key distribution system are as follows: A) Charlie uses a second laser to produce reference light, which he then sends to Alice and Bob. B) the detection device adds a second acousto-optic modulator to the public 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 light input port; D) Alice identifies the difference between the signal light of the first laser and the reference light by means of beat frequency, and then sends adjustment information to the first laser and the first acousto-optic modulator according to the difference information; E) Bob identifies the difference between the signal light and the reference light of the third optical device by means of beat frequency, and then sends adjustment information to the third laser and the third acousto-optic modulator according to the difference information; F) The detection device detects the signal optical power output by Alice in the public quantum signal. If the optical power is greater than the designed value, it means that there is a design flaw in the actual security of the measured quantum key distribution system. 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 designed value, it means that there is a design flaw in the actual security of the measured sub-key distribution system.

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 above-mentioned A) second laser is an ultra-stable laser.

4. The method according to claim 1, characterized in that: The adjustable range of the second AOM in B) above should be less than or equal to the adjustable range of the first AOM.

5. The method according to claim 1, characterized in that: The legal light input port in the above C) refers to the light input port that Alice and Bob actively open to receive reference light.

6. The method according to claim 1, characterized in that: The signal light of the first laser in D) above refers to the optical pulse used by Alice to carry encoded information during the quantum key distribution process.

7. The method according to claim 1, characterized in that: The signal light of the third laser in E) above refers to the optical pulse used by Bob to carry encoded information during the quantum key distribution process.

8. The method according to claim 1, characterized in that: The above F) in detecting the signal optical power output by Alice in the public quantum signal means that the detection device places a fifth beam splitter on the public quantum channel from Alice to Charlie; Alice's quantum light is split into two, one part is sent to Charlie, and the other part is used for optical power detection.

9. The method according to claim 1, characterized in that: The above G) in detecting the signal optical power output by Bob in the public quantum signal means that the detection device places a fourth beam splitter on the public quantum channel from Bob to Charlie; splits Bob's quantum light into two, one part is sent to Charlie, and the other part is used for optical power detection.

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