Trojan Light Attack Defense Method for Quantum Key Distribution and Transmitter Structure

Abstract

The present invention discloses a method for defending Trojan photon attacks in quantum key distribution and a corresponding sender structure that can be achieved only by using conventional devices without relying on any high-power devices, and can defend against various Trojan photon attacks in a simple and stable manner. At the same time, the present invention further proposes a specific implementation scheme for an optical fuse, which can accurately achieve the required optical fuse function with a simple process, so that the present invention can provide a sender structure that is easy to implement and has stable performance and can defend against various Trojan photon attacks.

Description

Technical Field

[0001] The present invention relates to the field of quantum secure communication, and particularly to a defense method against Trojan light attacks for quantum key distribution, and a transmitter structure for quantum key distribution that can defend against Trojan light attacks. Background Art

[0002] Quantum key distribution (QKD) is based on the principles of quantum mechanics. Due to the quantum no-cloning and uncertainty principles, it is a theoretically provable unconditionally secure key distribution system. In actual quantum key distribution devices, due to the imperfect characteristics of the devices, corresponding protection measures are also required to prevent information leakage.

[0003] For example, the imperfect characteristics of such devices may cause quantum key distribution devices to be vulnerable to strong light attacks. To defend against such strong light attacks, two basic defense ideas, namely passive defense and active defense, have been developed and studied.

[0004] In passive defense, an optical isolator is often introduced to reduce the light intensity when external input light enters the internal optical path. Since the bandwidth of an optical isolator is generally narrow, only dozens of nanometers, an optical filter is usually used in cooperation with the optical isolator to achieve a broadband optical isolation effect. At the same time, it is generally required that the optical isolator and the optical filter used have high power to prevent these optical devices from failing after being damaged by strong light, resulting in a reduction or even loss of the defense effect.

[0005] In active monitoring defense, an optical circulator is often set at the exit of the quantum key distribution device. Among them, the first, second, and third ports of the optical circulator are respectively connected to the optical path of the quantum key distribution device, an external optical fiber link, and a single-photon detector or a photodiode. Figure 1 Shows an active defense scheme for strong light attacks. As Figure 1 Shown, the first port of the optical circulator 38 is connected to the single-photon detector 37, and the second port 39 and the third port 40 are respectively connected to the internal encoding optical path and the external optical fiber link. In this scheme, the encoded signal light output from the internal encoding optical path can be output to the external optical fiber link through the second and third ports of the optical circulator 38, and the attack light input to the quantum key distribution device through the external optical fiber link enters the single-photon detector through the third and first ports of the optical circulator for monitoring.

[0006] In addition, a defense idea of setting an optical fuse in the quantum key distribution device to defend against strong light attacks has recently been proposed in the prior art.

[0007] However, the inventors have found through research that currently, a modulator is generally required at the transmitting end of a quantum key distribution device, and reflections are inevitable in the optical path. Therefore, if an eavesdropper inputs Trojan light from the outside of the transmitting end, when the Trojan light reaches the modulator, it will be modulated in the same way as the output light of the quantum key distribution device, thereby carrying modulation information. This Trojan light can be detected by the eavesdropper when it is reflected and output from the internal optical path of the transmitting end, which will cause information leakage. In this Trojan light attack, since the Trojan light is generated by the eavesdropper, theoretically, the eavesdropper can control the intensity of the Trojan light input to the quantum key distribution device, that is, the Trojan light can always be very strong, reaching the level of damaging the device; the Trojan light can also be very weak, only needing to be detectable after reflection and output; the Trojan light can also be very strong first to damage the device, and then adjusted to a lower light intensity level.

[0008] Obviously, for this type of Trojan light attack with complex attack behaviors, the above-known strong light defense ideas are not capable of meeting the defense requirements. Summary of the Invention

[0009] In view of the above problems existing in the prior art, the present invention discloses a method for defending against Trojan light attacks in quantum key distribution and a corresponding transmitting end structure that can be achieved only by using conventional devices without relying on any high-power devices, and can defend against various Trojan light attacks in a simple and stable manner. At the same time, the present invention further proposes a specific implementation scheme for an optical fuse, which can accurately achieve the required optical fuse function with a simple process, so that the present invention can provide a transmitting end structure that is easy to implement and has stable performance and can defend against various Trojan light attacks.

[0010] Specifically, a first aspect of the present invention relates to a transmitting end structure for quantum key distribution that can defend against Trojan light attacks, which includes a quantum state preparation module, a low-damage-threshold optical device, an optical beam splitter, and a first optical detection element;

[0011] The optical beam splitter has a first port, a second port, a third port, and a fourth port. Among them, the optical signal input through the first port is output from the second and fourth ports respectively according to a certain ratio, and the optical signal input through the second port is output from the first and third ports respectively according to a certain ratio;

[0012] The quantum state preparation module is used to generate signal light carrying encoded information and is arranged to be connected to the first port of the optical beam splitter;

[0013] The low-damage-threshold optical device is used to disconnect the optical path where it is located when the input optical signal exceeds its damage threshold and is arranged to be connected to the second port of the optical beam splitter;

[0014] The first optical detection element is arranged to be connected to the third port of the optical beam splitter and has a sensitivity S, and the sensitivity S is related to the power of the Trojan horse light allowed to enter the quantum state preparation module.

[0015] Furthermore, the quantum state preparation module includes a light source, an encoding unit, and an attenuation unit; and / or, a second photoelectric detection element is connected to the fourth port of the optical beam splitter.

[0016] Even further, the photoelectric detection element is a photodiode; and / or, the optical beam splitter is a 50:50 optical beam splitter.

[0017] Furthermore, the low damage threshold optical device includes an optical fiber having a smaller light guiding area than that of a common optical fiber. Preferably, the low damage threshold optical device includes a fused optical fiber.

[0018] Furthermore, the damage threshold of the low damage threshold optical device is determined according to the damage thresholds of the optical devices for implementing the quantum state preparation module, the optical beam splitter, and the first optical detection element.

[0019] The second aspect of the present invention relates to a method for defending against Trojan horse light attacks for quantum key distribution, which includes the following steps:

[0020] Determine the damage threshold Th of the low damage threshold optical device according to the damage thresholds of other optical devices for implementing the transmitting end;

[0021] When the power of the Trojan horse light exceeds the damage threshold Th, disconnect the optical path of the Trojan horse light reaching the other optical devices by means of the low damage threshold optical device; and,

[0022] When the power of the Trojan horse light does not exceed the damage threshold Th, monitor the power of the Trojan horse light entering the quantum state preparation module of the transmitting end and issue an alarm according to the monitoring result.

[0023] Furthermore, the optical beam splitter can be used to split the Trojan horse light passing through the low damage threshold optical device, so that a part of the Trojan horse light enters the quantum state preparation module, and at the same time, the other part of the Trojan horse light is used for power monitoring.

[0024] Even further, the power monitoring can be realized by using a photodiode, and the sensitivity S of the photodiode is determined according to the power of the Trojan horse light allowed to enter the quantum state preparation module.

[0025] Preferably, the damage threshold Th is 400 - 600 mW; and / or, the sensitivity S is selected such that, under the power of the Trojan horse light allowed to enter the quantum state preparation module, the power of the Trojan horse light output from the transmitting end is at least 70 dB weaker than the signal light output from the transmitting end.

[0026] Preferably, the defense method of the present invention can be implemented by means of the transmitter structure proposed by the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The following further describes in detail the specific embodiments of the present invention with reference to the drawings.

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 Shows the schematic diagram of the active defense strong light attack scheme of the prior art;

[0030] Figure 2 Shows the schematic diagram of the transmitter structure for quantum key distribution that can defend against Trojan horse optical attacks according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Hereinafter, the exemplary embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are provided by way of example to fully convey the spirit of the present invention to those skilled in the art to which the present invention pertains. Therefore, the present invention is not limited to the embodiments disclosed herein.

[0032] Figure 2 Shows the transmitter structure for quantum key distribution that can defend against Trojan horse optical attacks according to the present invention.

[0033] As Figure 2 shown, the transmitter structure may include a quantum state preparation module, a low damage threshold optical device, an optical beam splitter, and a first optical detection element.

[0034] The quantum state preparation module is used to generate signal light carrying encoded information, and it may include a light source, an encoding unit, and an attenuation unit.

[0035] The light source is used to provide an optical signal, which may be, for example, a continuous optical signal or a pulsed optical signal. As an example, the light source may be in the form of a laser, such as a semiconductor laser, as Figure 2 shown.

[0036] The encoding unit is used to encode the optical signal according to a quantum encoding protocol to obtain signal light carrying encoded information. For example, the quantum encoding protocol may include, but is not limited to, polarization encoding, phase encoding, time-phase encoding, MDI encoding, and the like.

[0037] The attenuation unit is used to attenuate the intensity of the signal light, for example, to obtain signal light at the single-photon level. As an example, the attenuation unit may include a tunable optical attenuator.

[0038] The optical beam splitter can be arranged between the attenuation unit of the quantum state preparation module and the low-damage-threshold optical device, and has a first port, a second port, a third port, and a fourth port, where: the optical signal input through the first port can be output from the second port and the fourth port respectively according to a certain ratio, and the optical signal input through the second port can be output from the first and third ports respectively according to a certain ratio.

[0039] Therefore, in the present invention, the optical beam splitter can be arranged such that its first port is connected to the quantum state preparation module (i.e., the attenuation unit), the second port is connected to the low-damage-threshold optical device, and the third port is connected to the first optical detection element. Therefore, the signal light output by the quantum state preparation module can be input through the first port of the optical beam splitter and is split into two components by the action of the optical beam splitter to be output through the second and fourth ports respectively; the Trojan horse light externally injected from the sending end can be input through the second port of the optical beam splitter and is split into two components by the action of the optical beam splitter to be output through the first and third ports respectively.

[0040] Under such an arrangement, preferably, a second optical detection element can also be arranged in the sending end structure, which is connected to the fourth port of the optical beam splitter and is used for monitoring the output optical intensity of the sending end or calibrating other parameters.

[0041] For the purpose of convenient monitoring, the optical beam splitter can preferably adopt a 50:50 optical beam splitter, so that the optical intensity of the Trojan horse light component detected by the first optical detection element is consistent with the Trojan horse light component entering the quantum state preparation module.

[0042] In the present invention, the damage threshold of the low-damage-threshold optical device can be determined according to the damage threshold of the conventional optical device used to implement the quantum state preparation module. Therefore, when the Trojan horse light externally injected from the sending end exceeds the damage threshold of the low-damage-threshold optical device, it will cause damage to the low-damage-threshold optical device, thereby disconnecting the optical path where it is located, thus preventing such strong Trojan horse light from entering the quantum state preparation module to cause damage to the optical devices therein and interrupting the normal operation of the sending end, ensuring the security of the key. It can be seen that by setting the low-damage-threshold optical device in this way, strong Trojan horse light can be effectively prevented from entering the quantum state preparation module for attack, so that conventional optical devices can be used in the quantum state preparation module without using special high-power devices.

[0043] Furthermore, the present invention also proposes a convenient and reliable implementation method for the low-damage-threshold optical device.

[0044] Specifically, the inventors propose that for an optical signal with a determined energy, a higher power density will be formed at an optical fiber with a smaller light guiding area, thereby triggering damage first and achieving the disconnection of the optical path. Therefore, the present invention proposes to use an optical fiber with a smaller light guiding area than that of a common optical fiber (such as a common single-mode optical fiber) to implement a low-damage-threshold optical device. Thus, by means of a mature optical fiber preparation process, the damage threshold of the low-damage-threshold optical device can be conveniently and precisely controlled simply by controlling the light guiding area of the optical fiber.

[0045] As a preferred example, the low-damage-threshold optical device can be implemented by means of a fused optical fiber. Among them, by stretching the optical fiber by melting, when the volume is the same, the stretching length is approximately inversely proportional to the area. Therefore, the fused optical fiber can obtain a smaller area than that of a common optical fiber, thereby achieving a higher power density and obtaining a lower damage threshold.

[0046] For example, by controlling the light guiding area of the fused optical fiber, its damage threshold can be made lower than 1 / 2 of the damage threshold of a common optical fiber.

[0047] Therefore, in the quantum key distribution device of the present invention, by simply selecting a fused optical fiber with a suitable damage threshold, it is allowed to disconnect the optical path when the optical intensity of the externally input Trojan horse light exceeds this damage threshold, preventing the Trojan horse light from entering the quantum state preparation module and forming a strong light attack on other optical devices such as the first optical detection element or optical transmission element, ensuring the security of the key, and allowing the use of conventional optical devices within the sending end structure without the need to select special high-power devices, thereby reducing the cost of the quantum key distribution device and improving its stability.

[0048] In the sending end structure of the present invention, the damage threshold of the low-damage-threshold optical device can be 400 - 600 mW, preferably 500 mW. Therefore, if the optical intensity of the Trojan horse light exceeds 500 mW, it will cause damage to the low-damage-threshold optical device, thereby disconnecting the optical path for the Trojan horse light to enter the quantum state preparation module and protecting the security of the internal optical devices and the key. Since it can be ensured that the power of the Trojan horse light reaching the quantum state preparation module, the optical beam splitter, and the optical detection element will not be stronger than 500 mW, the use of conventional optical devices is allowed without the need for special high-power optical devices.

[0049] In the sending end structure of the present invention, by organically combining the low-damage-threshold optical device and the first optical detection element by means of an optical beam splitter, it is possible to detect the weak Trojan horse light attack behavior with the help of the first optical detection element while resisting the strong Trojan horse light attack, so as to provide an alarm when under a Trojan horse light attack. Thus, the sending end structure is allowed to provide the ability to resist various Trojan horse light attacks.

[0050] As described above, in the transmitting - end structure of the present invention, the Trojan horse optical power reaching the first optical detection element can be limited, so a conventional optical device can be used to implement the first optical detection element.

[0051] As an example, the first optical detection element can be implemented using a conventional photodiode, which is sufficient to meet the requirements for resisting weak Trojan horse optical attacks.

[0052] For a better understanding of the present invention, the working principle of the transmitting - end structure will be described below in conjunction with Figure 2 the specific embodiments shown, where the optical splitter is a 50:50 optical splitter.

[0053] The conventional photodiode used to implement the first optical detection element can have a sensitivity of - 60 dBm. Therefore, in the transmitting - end structure of the present invention, when the Trojan horse optical power entering the quantum state preparation module is - 60 dBm, the presence of the Trojan horse optical can be detected and an alarm can be issued to interrupt the quantum key distribution process to ensure the security of the key.

[0054] Currently, the repetition frequency of quantum key distribution devices is relatively high, about 1 GHz, and at the same time, the average number of photons per pulse needs to be less than 1 photon. Therefore, the optical power output by the transmitting end of a quantum key distribution device is generally lower than - 70 dBm.

[0055] Most quantum key distribution devices use a semiconductor laser for communication as the light source, and its power in continuous light output is generally about + 10 dBm. Therefore, during pulse modulation, even if the single - pulse time - domain width is conservatively estimated to be 10 ps, at a repetition frequency of 1 GHz, its equivalent duty cycle is estimated to be 1 / 100, and the optical power also needs to be greater than - 10 dBm. Generally speaking, without using an optical isolator, the Trojan horse optical needs to experience at least 80 dB of attenuation from entering the transmitting end to being reflected and output. Therefore, when the Trojan horse optical entering the quantum state preparation module is weaker than - 60 dBm, the reflected light that the attacker can obtain is at least 70 dB weaker than the signal light carrying information output by the transmitting end, that is, the information obtained by the attacker through the Trojan horse optical is 1 / 10 of the original information. 7 Below, it has been almost impossible to obtain effective information. For this reason, in the transmitting - end structure of the present invention, a conventional photodiode is used to detect and give early warning of the Trojan horse optical, and the Trojan horse optical attack can be effectively defended without using an isolator and a filter.

[0056] In summary, in the present invention, an original solution is proposed to achieve a scheme for defending against complex Trojan optical attacks by organically combining a conventional optical beam splitter and optical detection elements with a low damage threshold optical device. This allows for defending against various Trojan optical attack methods (such as strong light, weak light, or strong-then-weak attacks) without the need for any high-power devices, only by relying on conventional optical devices, and ensuring the safety of the internal optical devices at the sending end in a simple, stable, and effective manner, ultimately ensuring the security of quantum keys. In addition, a simple and precise implementation scheme for the low damage threshold optical device is further proposed, that is, the low damage threshold optical device is realized in the form of a fused optical fiber.

[0057] Furthermore, the present invention also provides a method for defending against Trojan optical attacks for quantum key distribution, which can be implemented by means of the sending end structure of the present invention.

[0058] In this defense method, the damage threshold Th of the low damage threshold optical device can be determined according to the damage threshold of the conventional optical device used to implement the sending end, and the low damage threshold optical device is set at the output port of the sending end. Therefore, when the Trojan optical power entering the sending end exceeds the damage threshold Th, the low damage threshold optical device can be used to disconnect the optical path for the Trojan optical to further enter the interior of the sending end (i.e., the conventional optical device used to implement the sending end), thereby avoiding strong Trojan optical light from forming a strong light attack on the conventional optical device inside the sending end.

[0059] Moreover, when the Trojan optical power entering the sending end is less than the damage threshold Th, the Trojan optical power entering the quantum state preparation module can be monitored, and an alarm can be issued according to the monitoring result.

[0060] According to the present invention, a conventional photodiode can be used to monitor the Trojan optical power entering the quantum state preparation module. Among them, an optical beam splitter can be used to split the Trojan optical light passing through the low damage threshold optical device, so that a part of the Trojan optical light enters the photodiode and the other part of the Trojan optical light enters the quantum state preparation module, thereby monitoring the Trojan optical power entering the quantum state preparation module.

[0061] The sensitivity S of the photodiode can be determined according to the maximum value of the Trojan optical power allowed to enter the quantum state preparation module. Those skilled in the art can understand that even if the Trojan optical light below this power maximum enters the quantum state preparation module and is modulated, the light intensity when it finally reflects from the sending end will not be sufficient for the eavesdropper to obtain the modulation information. For example, the light intensity of the reflected output Trojan optical light is at least 70 dB weaker than the signal optical light output from the sending end.

[0062] By means of the method for defending against Trojan optical attacks of the present invention, the sending end structure can be implemented using conventional optical devices, and the defense process is simple and reliable, suitable for defending against various Trojan optical attack methods.

[0063] Although the present invention has been described by way of specific embodiments in conjunction with the accompanying drawings, it is readily appreciated by those skilled in the art that the above embodiments are merely exemplary and are used to illustrate the principles of the present invention, which will not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications and equivalent replacements to the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. A transmitting - end structure for quantum key distribution that can defend against Trojan optical attacks, which includes a quantum state preparation module, a low - damage - threshold optical device, an optical beam splitter, and a first optical detection element; The optical beam splitter has a first port, a second port, a third port, and a fourth port, where, The optical signal input through the first port is output from the second and fourth ports respectively according to a certain ratio, and the optical signal input through the second port is output from the first and third ports respectively according to a certain ratio; The quantum state preparation module is used to generate signal light carrying encoded information and is arranged to be connected to the first port of the optical beam splitter; The low damage threshold optical device is used to disconnect the optical path where it is located when the input optical signal exceeds its damage threshold and is arranged to be connected to the second port of the optical beam splitter; The first optical detection element is arranged to be connected to the third port of the optical beam splitter and has a sensitivity S, and the sensitivity S is related to the power of the Trojan horse light allowed to enter the quantum state preparation module.

2. The transmitting - end structure according to claim 1, wherein, The quantum state preparation module includes a light source, an encoding unit and an attenuation unit; and / or, a second photoelectric detection element is connected to the fourth port of the optical beam splitter.

3. The transmitting - end structure according to claim 1 or 2, wherein, The photoelectric detection element is a photodiode; and / or, the optical beam splitter is a 50:50 optical beam splitter.

4. The transmitting - end structure according to claim 1, wherein, The low damage threshold optical device includes an optical fiber having a smaller light guiding area than ordinary optical fibers.

5. The transmitting - end structure according to claim 4, wherein, The low damage threshold optical device includes a fused optical fiber.

6. The transmitting - end structure according to claim 1, wherein, The damage threshold of the low damage threshold optical device is determined according to the damage thresholds of the optical devices for implementing the quantum state preparation module, the optical beam splitter and the first optical detection element.

7. A method for defending against Trojan optical attacks in quantum key distribution, which is implemented by means of the transmitting - end structure according to any one of claims 1 - 6, and includes the following steps: Determine the damage threshold Th of the low damage threshold optical device according to the damage thresholds of other optical devices for implementing the sending end; When the power of the Trojan horse light exceeds the damage threshold Th, disconnect the optical path of the Trojan horse light reaching the other optical devices by means of the low damage threshold optical device; and, When the power of the Trojan horse light does not exceed the damage threshold Th, monitor the power of the Trojan horse light entering the quantum state preparation module of the sending end and issue an alarm according to the monitoring result.

8. The defense method according to claim 7, wherein, Use an optical beam splitter to split the Trojan horse light passing through the low damage threshold optical device, so that a part of the Trojan horse light enters the quantum state preparation module, and at the same time, the other part of the Trojan horse light is used for power monitoring.

9. The defense method according to claim 8, wherein, Use a photodiode to realize the power monitoring, and the sensitivity S of the photodiode is determined according to the power of the Trojan horse light allowed to enter the quantum state preparation module.

10. The defense method according to claim 9, wherein, The damage threshold Th is 400 - 600 mW; and / or, the sensitivity S is selected such that, under the power of the Trojan horse light allowed to enter the quantum state preparation module, the power of the Trojan horse light output from the sending end is at least 70 dB weaker than the signal light output from the sending end.

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