Random phase modulation FSO channel key distribution system and method

Abstract

The invention relates to a random phase modulation FSO channel key distribution system and method, and belongs to the technical field of information security. According to the invention, the liquid crystal spatial light modulator is used for randomly changing the spatial phase of the optical signal, so that the power of the optical signal finally incident on the detector is randomly changed. According to the invention, the initial random source used for generating the shared key, random signals output by two legal end machines and used for controlling the liquid crystal spatial light modulator to carry out optical phase modulation, and the random entropy of the random signals in unit time can be controlled by the legal end machines and is not limited by the change rate of the external environment of a channel. According to the method, information theory security key distribution of the classical FSO channel can be realized, an eavesdropper does not need to be secreted by virtue of atmospheric random light fading mixing, and the method can be normally implemented in an inter-satellite optical channel. Compared with quantum key distribution, the method does not use a quantum device, is compatible with classical optical communication equipment, and is lower in implementation cost.

Description

Technical Field

[0001] The invention belongs to the technical field of information security, and in particular relates to a random phase modulation FSO channel key distribution system and method. Background Art

[0002] The free-space optical (FSO) channel combined with quantum key distribution (QKD) can realize key sharing between two separated terminals, providing support for users to achieve flexible, high-speed and secure communication. A free-space optical channel refers to a channel that transmits optical signals directly in free space without the assistance of optical fiber. For example, a random fading perturbation secret atmospheric optical channel key distribution method disclosed in the Chinese invention patent with application number 202311330250.7, in terminal A, an electro-optical modulator is used to randomly change the amplitude of the optical signal; in terminal B, the amplitude of the optical signal output by the electro-optical modulator does not change with time. On the one hand, this scheme essentially only modulates the amplitude of the optical signal transmitted by terminal A, but does not modulate the amplitude of the optical signal transmitted by terminal B. On the other hand, due to the use of an electro-optical modulator, this scheme can only randomly change the amplitude of the transmitted optical signal, and cannot arbitrarily change the spatial phase of the transmitted optical signal. This method uses an electro-optic modulator to multiplicatively modulate the amplitude of the transmitted optical signal, and at the same time uses the atmospheric random light fading perturbation to achieve the purpose of information-theoretic security key distribution using the classical atmospheric optical channel. However, the method disclosed in this patent requires that the optical channel must be affected by atmospheric turbulence disturbances in order to achieve perturbation secrecy. However, not all FSO channels are affected by atmospheric turbulence disturbances. For example, the intersatellite optical transmission channel does not have atmospheric turbulence disturbances. Therefore, it is of great significance to design a free-space classical optical channel key distribution system and method that does not rely on atmospheric turbulence disturbances. Summary of the invention

[0003] The present invention aims to solve the technical problem that the FSO channel key distribution method in the prior art needs to rely on atmospheric random light fading disturbance to achieve secrecy from eavesdroppers, that is, to prevent illegal eavesdroppers from obtaining the distributed key information, and if the FSO channel is not affected by atmospheric turbulence disturbance, it is impossible to effectively perform information-theoretic secure key distribution, and provides a random phase modulation FSO channel key distribution system and method. The key distribution system of the present invention can realize information-theoretic secure key distribution of the classic FSO channel that is independent of atmospheric turbulence disturbance.

[0004] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0005] A random phase modulation FSO channel key distribution system includes a terminal A and a terminal B;

[0006] The terminal A comprises, in the direction of the optical path, a laser A, a transceiver common mode coupling module A, a convex lens A1, a spatial optical phase modulator A, a convex lens A2 and an optical transceiver aperture A; the transceiver common mode coupling module A is also connected in sequence to a detector A and a computer A;

[0007] The terminal B includes, in the direction of the optical path, a laser B, a transceiver common mode coupling module B, a convex lens B1, a spatial optical phase modulator B, a convex lens B2 and an optical transceiver aperture B; the transceiver common mode coupling module B is also connected to a detector B and a computer B in sequence;

[0008] The optical signal emitted by laser A is incident on the transmitting light input port of the transceiver common mode coupling module A through a single-mode optical fiber, and is emitted from the transceiver common port of the transceiver common mode coupling module A. The emitted optical signal is transformed by convex lens A1 and then incident on spatial optical phase modulator A. The optical signal emitted from spatial optical phase modulator A is further transformed by convex lens A2 and then enters the free space optical channel for transmission through optical transceiver hole A. After reaching terminal B, the optical signal enters optical transceiver hole B and is transformed by convex lens B2 and then incident on spatial optical phase modulator B. The optical signal emitted from spatial optical phase modulator B is transformed by convex lens B1 and then incident on the transceiver common port of the transceiver common mode coupling module B. The optical signal emitted from the receiving light output port of the transceiver common mode coupling module B is incident on detector B through a single-mode optical fiber. The electrical signal output by detector B is transmitted to the acquisition card of computer B and is sampled and quantized into a digital signal and stored in computer B.

[0009] The optical signal emitted by laser B is incident on the transmitting light input port of the transceiver common mode coupling module B through the single-mode optical fiber, and is emitted from the transceiver common port of the transceiver common mode coupling module B. The emitted optical signal is transformed by the convex lens B1 and incident on the spatial optical phase modulator B. The optical signal emitted from the spatial optical phase modulator B is transformed by the convex lens B2 and enters the free space optical channel for transmission through the optical transceiver hole B. After reaching the terminal A, it enters the optical transceiver hole A and is transformed by the convex lens A2 and incident on the spatial optical phase modulator A. The optical signal emitted from the spatial optical phase modulator A is transformed by the convex lens A1 and incident on the transceiver common port of the transceiver common mode coupling module A. The optical signal emitted from the receiving light output port of the transceiver common mode coupling module A is incident on the detector A through the single-mode optical fiber. The electrical signal output by the detector A is transmitted to the acquisition card of the computer A and is sampled and quantized into a digital signal and stored in the computer A.

[0010] The random phase control signal output by computer B is transmitted to the control port of spatial optical phase modulator B, and is used to control the spatial phase modulation of the optical signal incident on spatial optical phase modulator B; the random phase control signal output by computer A is transmitted to the control port of spatial optical phase modulator A, and is used to control the spatial phase modulation of the optical signal incident on spatial optical phase modulator A.

[0011] In the above technical solution, both the spatial light phase modulator A and the spatial light phase modulator B use reflective liquid crystal spatial light modulators.

[0012] In the above technical solution, the transceiver common-mode coupling module A and the transceiver common-mode coupling module B are both implemented using an optical fiber circulator.

[0013] In the above technical solution, the detector A and the detector B are both PIN photodetectors or APD photodetectors.

[0014] In the above technical solution, the computer A and the computer B communicate with each other via the Internet.

[0015] A random phase modulation FSO channel key distribution method, the applicable system of which is the random phase modulation FSO channel key distribution system, comprises the following steps:

[0016] Step S1, make terminal A and terminal B work normally;

[0017] Computer A starts from time t0 and outputs a random phase control signal of spatial optical phase modulator A every time τs, so as to control spatial phase modulation generated by spatial optical phase modulator A on the incident optical signal;

[0018] Computer B starts from time t0 and outputs a random phase control signal of spatial optical phase modulator B every time τs, so as to control spatial phase modulation of the incident optical signal by spatial optical phase modulator B;

[0019] Computer A starts from time t0 and samples the electrical signal output by detector A every time τs to obtain a sampled measurement value MsA; Computer A obtains a total of Nt+1 sampled measurement values ​​MsA at time Nt×τs+t0, where Nt is a positive integer; These Nt+1 sampled measurement values ​​MsA are stored in a list LISTA in the memory of computer A in the order of their acquisition time; The i-th sampled measurement value MsA is obtained at time (i-1)×τs+t0, where i=1,2,3,…,Nt+1;

[0020] Computer B starts sampling and measuring the electrical signal output by detector B once every τs from time t0 to obtain a sampling measurement value MsB; Computer B obtains a total of Nt+1 sampling measurement values ​​MsB at time Nt×τs+t0, where Nt is a positive integer; These Nt+1 sampling measurement values ​​MsB are stored in a list LISTB in the memory of computer B in the order of their acquisition time; The i-th sampling measurement value MsB is obtained at time (i-1)×τs+t0, where i=1,2,3,…,Nt+1;

[0021] Step S2: perform the following steps in computer A:

[0022] Step S201: Treat the values ​​of all elements in the list LISTA as random observations, calculate the corresponding empirical cumulative distribution function FA(x) using a program in computer A, and take the value of x that makes FA(x) closest to 0.5 as the decision threshold TxA; create a list KeyLA in the memory of computer A, and set the list KeyLA to be empty;

[0023] Step S202: For i=1, 2, 3, ..., Nt+1, perform the following operations in sequence:

[0024] Let MsAi represent the value of the i-th element of the list LISTA; if the value of MsAi is greater than the decision threshold TxA, then add an element to the end of the list KeyLA and set the value of the element equal to 1, otherwise add an element to the end of the list KeyLA and set the value of the element equal to 0;

[0025] Step S3: perform the following steps in computer B:

[0026] Step S301: Treat the values ​​of all elements in the list LISTB as random observations, calculate the corresponding empirical cumulative distribution function FB(x) using a program in computer B, and take the value of x that makes FB(x) closest to 0.5 as the decision threshold TxB; create a list KeyLB in the memory of computer B, and set the list KeyLB to be empty;

[0027] Step S302: For i=1, 2, 3, ..., Nt+1, perform the following operations in sequence:

[0028] Let MsBi represent the value of the i-th element of the list LISTB; if the value of MsBi is greater than the decision threshold TxB, then add an element to the end of the list KeyLB and set the value of the element equal to 1, otherwise add an element to the end of the list KeyLB and set the value of the element equal to 0;

[0029] Step S4: Use the error estimation, key negotiation, and error checking techniques in the post-processing of quantum key distribution to correct the inconsistent bits in the bit sequences of the original shared keys stored in the list KeyLA and the list KeyLB, so that computer A and computer B obtain a consistent shared key bit sequence.

[0030] In the above technical solution, τs=1 millisecond, Nt=10000.

[0031] The beneficial effects of the present invention are:

[0032] The random phase modulation FSO channel key distribution system of the present invention can realize the information theory security key distribution of the classical FSO channel, and does not need to rely on the atmospheric random light fading disturbance to conceal the eavesdropper, and can be normally implemented in the intersatellite optical channel. Compared with quantum key distribution, the present invention does not need to use quantum devices and is compatible with classical optical communication equipment, and has a lower implementation cost.

[0033] The initial random source of the random phase modulation FSO channel key distribution system and method of the present invention comes from the random control signals of the spatial optical phase modulator A and the spatial optical phase modulator B output by computer A and computer B, and the size of the random entropy per unit time can be controlled by the legal terminal, and the final shared key generation rate is not subject to the rate of change of the channel external environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0035] Figure 1 It is a structural schematic diagram of the random phase modulation FSO channel key distribution system of the present invention.

[0036] The reference numerals in the figures indicate:

[0037] 101-laser A, 102-spatial optical phase modulator A, 103-optical transceiver port A, 104-transceiver common mode coupling module A, 105-detector A, 106-computer A, 107-convex lens A1, 108-convex lens A2;

[0038] 201 - laser B, 202 - spatial light phase modulator B, 203 - optical transceiver port B, 204 - transceiver common mode coupling module B, 205 - detector B, 206 - computer B, 207 - convex lens B1, 208 - convex lens B2. DETAILED DESCRIPTION

[0039] In order to make the features and advantages of the random phase modulation FSO channel key distribution system and method of the present invention more clear, the present invention is further described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0040] In this embodiment, both computer A 106 and computer B 206 are connected to the Internet, and computer A 106 and computer B 206 can communicate with each other through the Internet to perform error estimation, key negotiation, and error checking operations on the original shared key through the Internet channel.

[0041] In this embodiment, both detector A 105 and detector B 205 are PIN photoelectric detectors. In this embodiment, terminal A and terminal B are 10 kilometers apart and can directly see each other.

[0042] This embodiment uses the error estimation, key negotiation, and error checking techniques used in the post-processing of quantum key distribution to perform inconsistent bit error correction on the original shared random bit sequences extracted by the two optical transceivers, and ensure that the shared random bit sequences finally obtained become shared random bit sequences that can be used in practice. For example, the paper published in the Journal of Cryptography, Vol. 2, No. 2, 2015, pp. 113-121, provides a detailed introduction to the error estimation, key negotiation, and error checking operations in the post-processing of quantum key distribution.

[0043] In this embodiment, the transceiver common mode coupling module A104 and the transceiver common mode coupling module B204 use the method described in the paper "Optics Express" Vol. 26, No. 13, 2018, pp. 16422-16441 to ensure that the bidirectional channel between terminal A and terminal B is reciprocal. The Chinese invention patent with application number 201911248203.1 also introduced the transceiver common mode coupling technology. The description in the paper "Journal of Optical Communications and Networking" Vol. 4, No. 12, pp. 947-954, 2012 also shows that even if there is a spatial optical phase modulation module between the transceiver common mode coupling module A104 and the transceiver common mode coupling module B204, the reciprocity of the bidirectional channel can be ensured. Specifically, the transceiver common mode coupling module A104 and the transceiver common mode coupling module B204 are implemented using an optical fiber circulator, and the optical fiber is a single-mode optical fiber, which is consistent with the Chinese invention patent with application number 201611114333.2. Figure 1The optical fiber circulator 1 104 and the optical fiber circulator 2 204 are the same, the function of the transmission light input port of the transceiver common mode coupling module A 104 and the transceiver common mode coupling module B 204 of the present invention is similar to the port A201 described in the Chinese invention patent with application number 201611114333.2, the function of the transceiver common mode coupling module A 104 and the transceiver common mode coupling module B 204 of the present invention is similar to the port A202 described in the Chinese invention patent with application number 201611114333.2, and the function of the reception light output port of the transceiver common mode coupling module A 104 and the transceiver common mode coupling module B 204 of the present invention is similar to the port A203 described in the Chinese invention patent with application number 201611114333.2.

[0044] In this embodiment, both the spatial light phase modulator A 102 and the spatial light phase modulator B 202 use a reflective liquid crystal spatial light modulator; the function of the liquid crystal spatial light modulator is to add a spiral phase to the light field of the incident light signal, which is to multiply the light field of the incident light signal by a factor exp(i·l·θ) in mathematics, where l represents an integer randomly taking a value between [-2,2], θ represents an azimuth angle, and i represents an imaginary unit. The paper of "Optics Letters" Vol. 37, No. 17, 2012, pp. 3735-3737 describes the idea of ​​adding a spiral phase to the light field of the incident light signal; this embodiment refers to the method in the paper and uses a liquid crystal spatial light modulator to add a spiral phase to the light field of the incident light signal. In this embodiment, l is a random number, so the multiplicative factor exp(i·l·θ) plays a role in randomly adding a spiral phase to the light field of the incident light signal. Computer A 106 and computer B 206 independently and randomly select the value of l, and then control spatial optical phase modulator A 102 and spatial optical phase modulator B 202 to add a random spiral phase to the light field of their respective incident optical signals. Computer A 106, computer B 206, spatial optical phase modulator A 102 and spatial optical phase modulator B202 are all inside the legal terminal. Under the condition that the legal terminal is not discovered, the eavesdropper cannot obtain the information generated inside the legal terminal, that is, the eavesdropper does not know the specific l value selected by computer A 106 and computer B 206 at a specific moment. Before detecting the optical signal sent from the other party, the legal terminal adds a random spiral phase known only to the legal terminal to the optical field of the optical signal, which changes the spatial phase of the optical signal, resulting in random changes in the power of the optical signal emitted from the receiving optical output port of the transceiver common mode coupling module A 104 and the transceiver common mode coupling module B204, and this random change is invisible to the eavesdropper.

[0045] The calculation method of the decision threshold in step S201 and step S301 of this embodiment is the same as the calculation method of the decision threshold in step Step 403-1 and step Step 502-1 of the Chinese invention patent with application number 202311330250.7.

[0046] The present invention is described in detail below with reference to the accompanying drawings.

[0047] like Figure 1 As shown, the random phase modulation FSO channel key distribution system of the present invention includes a terminal A and a terminal B; the terminal A includes a laser A 101, a spatial light phase modulator A 102, an optical transceiver port A 103, a transceiver common mode coupling module A 104, a detector A 105, a computer A 106, a convex lens A1 107, and a convex lens A2 108. The terminal B includes a laser B 201, a spatial light phase modulator B 202, an optical transceiver port B 203, a transceiver common mode coupling module B 204, a detector B 205, a computer B 206, a convex lens B1 207, and a convex lens B2 208.

[0048] The laser A101, the transceiver common mode coupling module A104, the convex lens A1107, the spatial light phase modulator A102, the convex lens A2108 and the optical transceiver hole A103 are sequentially arranged in the direction of the optical path; the transceiver common mode coupling module A104 is also connected to the detector A105 and the computer A106 in sequence.

[0049] The laser B 201, the transceiver common mode coupling module B 204, the convex lens B1 207, the spatial light phase modulator B202, the convex lens B2 208 and the optical transceiver hole B 203 are sequentially arranged in the light path direction; the transceiver common mode coupling module B204 is also connected to the detector B 205 and the computer B 206 in sequence.

[0050] The optical signal emitted by the laser A 101 is incident on the transmitting light input port of the transceiver common mode coupling module A 104 through the single-mode optical fiber, and is emitted from the transceiver common port of the transceiver common mode coupling module A 104. The optical signal emitted from the transceiver common port of the transceiver common mode coupling module A 104 is transformed by the convex lens A1 107 and incident on the spatial optical phase modulator A 102. The optical signal emitted from the spatial optical phase modulator A 102 is further transformed by the convex lens A2 108 and enters the free space optical channel for transmission through the optical transceiver hole A 103. After reaching the terminal B, it enters the optical transceiver hole B 203 and is transformed by the convex lens B2 208 and incident on the spatial optical phase modulator B 202. The optical signal emitted from the spatial optical phase modulator B 202 is transformed by the convex lens B1 207 and incident on the transceiver common port of the transceiver common mode coupling module B 204. The optical signal emitted from the receiving optical output port of 204 is incident on the detector B 205 through the single-mode optical fiber. The electrical signal output by the detector B 205 is transmitted to the acquisition card of the computer B 206 and is sampled and quantized into a digital signal and stored in the computer B 206.

[0051] The optical signal emitted by the laser B 201 is incident on the transmitting light input port of the transceiver common mode coupling module B 204 through the single-mode optical fiber, and is emitted from the transceiver common port of the transceiver common mode coupling module B 204. The optical signal emitted from the transceiver common port of the transceiver common mode coupling module B 204 is transformed by the convex lens B1 207 and incident on the spatial optical phase modulator B 202. The optical signal emitted from the spatial optical phase modulator B 202 is further transformed by the convex lens B2 208 and enters the free space optical channel for transmission through the optical transceiver hole B 203. After reaching the terminal A, it enters the optical transceiver hole A 103 and is transformed by the convex lens A2 108 and incident on the spatial optical phase modulator A 102. The optical signal emitted from the spatial optical phase modulator A102 is transformed by the convex lens A1107 and incident on the transceiver common port of the transceiver common mode coupling module A 104. The optical signal emitted from the receiving optical output port of 104 is incident on the detector A 105 through the single-mode optical fiber. The electrical signal output by the detector A 105 is transmitted to the acquisition card of the computer A 106 and is sampled and quantized into a digital signal and stored in the computer A 106.

[0052] The random phase control signal output by computer B 206 is transmitted to the control port of spatial optical phase modulator B 202, and is used to control the spatial phase modulation of the optical signal incident on spatial optical phase modulator B 202. The random phase control signal output by computer A106 is transmitted to the control port of spatial optical phase modulator A 102, and is used to control the spatial phase modulation of the optical signal incident on spatial optical phase modulator A 102. There is spatial light to single-mode fiber coupling between convex lens A1 107 and the transceiver common port of transceiver common mode coupling module A104. There is spatial light to single-mode fiber coupling between convex lens B1 207 and the transceiver common port of transceiver common mode coupling module B204.

[0053] The random phase modulation FSO channel key distribution method of the present invention is applicable to the random phase modulation FSO channel key distribution system of the present invention, and comprises the following steps:

[0054] Step S1, the first step of the method is to make the terminal A and the terminal B work normally, and the specific operations include:

[0055] Make the laser A 101, the spatial light phase modulator A 102, the optical transceiver port A 103, the transceiver common mode coupling module A 104, the detector A 105, the computer A 106, the laser B 201, the spatial light phase modulator B 202, the optical transceiver port B 203, the transceiver common mode coupling module B 204, the detector B 205, and the computer B 206 work normally.

[0056] Computer A106 starts from time t0 and outputs a random phase control signal of spatial optical phase modulator A102 every time τs, which is used to control spatial phase modulation of the incident optical signal generated by spatial optical phase modulator A102. Computer B206 starts from time t0 and outputs a random phase control signal of spatial optical phase modulator B202 every time τs, which is used to control spatial phase modulation of the incident optical signal generated by spatial optical phase modulator B202.

[0057] Computer A 106 starts from time t0 and samples the electrical signal output by detector A 105 every time τs to obtain a sampled measurement value MsA; computer A 106 obtains a total of Nt+1 sampled measurement values ​​MsA at time Nt×τs+t0, where Nt is a positive integer; these Nt+1 sampled measurement values ​​MsA are saved in a list LISTA in the memory of computer A 106 in the order of their acquisition time; the i-th sampled measurement value MsA is obtained at time (i-1)×τs+t0, where i=1,2,3,…,Nt+1.

[0058] Computer B 206 starts from time t0 and samples the electrical signal output by detector B 205 every time τs to obtain a sampled measurement value MsB; computer B 206 obtains a total of Nt+1 sampled measurement values ​​MsB at time Nt×τs+t0, where Nt is a positive integer; these Nt+1 sampled measurement values ​​MsB are saved in a list LISTB in the memory of computer B 206 in the order of their acquisition time; the i-th sampled measurement value MsB is obtained at time (i-1)×τs+t0, where i=1,2,3,…,Nt+1.

[0059] Step S2, the second step of the method, performs the following operations in computer A106:

[0060] Step S201: Treat the values ​​of all elements of the list LISTA as random observations, calculate the corresponding empirical cumulative distribution function FA(x) using a program in the computer A 106, and take the value of x that makes FA(x) closest to 0.5 as the decision threshold TxA; create a list KeyLA in the memory of the computer A 106; set the list KeyLA to be empty;

[0061] Step S202: For i=1, 2, 3, ..., Nt+1, perform the following operations in sequence:

[0062] Let MsAi represent the value of the i-th element of the list LISTA; if the value of MsAi is greater than the decision threshold TxA, then add an element to the end of the list KeyLA and set the value of the element equal to 1, otherwise add an element to the end of the list KeyLA and set the value of the element equal to 0.

[0063] Step S3, the third step of the method, performs the following operations in computer B 206:

[0064] Step S301: Treat the values ​​of all elements of the list LISTB as random observations, calculate the corresponding empirical cumulative distribution function FB(x) using a program in the computer B 206, and take the value of x that makes FB(x) closest to 0.5 as the decision threshold TxB; create a list KeyLB in the memory of the computer B 206; set the list KeyLB to be empty;

[0065] Step S302: For i=1, 2, 3, ..., Nt+1, perform the following operations in sequence:

[0066] Let MsBi represent the value of the i-th element of the list LISTB; if the value of MsBi is greater than the decision threshold TxB, then add an element to the end of the list KeyLB and set the value of the element equal to 1, otherwise add an element to the end of the list KeyLB and set the value of the element equal to 0.

[0067] Step S4, the fourth step of the method utilizes error estimation, key negotiation, and error checking techniques in the post-processing of quantum key distribution to correct inconsistent bits in the bit sequences of the original shared keys stored in the list KeyLA and the list KeyLB, so that computer A 106 and computer B 206 obtain a consistent shared key bit sequence.

[0068] In this embodiment, τs = 1 millisecond, and Nt = 10000. A list is a concept in computer programming. It is a collection of a series of elements arranged in order from front to back and is a container for storing data.

[0069] In summary, the random phase modulation FSO channel key distribution system of the present invention can realize the information theory security key distribution of the classical FSO channel, and does not need to rely on the atmospheric random light fading perturbation to conceal the eavesdropper, and can be normally implemented in the intersatellite optical channel. Compared with quantum key distribution, the present invention does not need to use quantum devices and is compatible with classical optical communication equipment, and has a lower implementation cost.

[0070] The initial random source of the random phase modulation FSO channel key distribution system and method of the present invention comes from the random control signals of the spatial optical phase modulator A and the spatial optical phase modulator B output by computer A and computer B, and the size of the random entropy per unit time can be controlled by the legal terminal, and the final shared key generation rate is not subject to the rate of change of the channel external environment.

[0071] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A random phase modulation FSO channel key distribution system, characterized in that: Including terminal A and terminal B; The terminal A comprises, in order in the direction of the optical path: a laser A (101), a transceiver common mode coupling module A (104), a convex lens A1 (107), a spatial optical phase modulator A (102), a convex lens A2 (108) and an optical transceiver aperture A (103); the transceiver common mode coupling module A (104) is also connected in order to a detector A (105) and a computer A (106); The terminal B comprises, in order in the direction of the optical path: a laser B (201), a transceiver common mode coupling module B (204), a convex lens B1 (207), a spatial optical phase modulator B (202), a convex lens B2 (208) and an optical transceiver aperture B (203); the transceiver common mode coupling module B (204) is also connected in order to a detector B (205) and a computer B (206); The optical signal emitted by the laser A (101) is incident on the transmitting light input port of the transceiver common mode coupling module A (104) through the single mode optical fiber, and is emitted from the transceiver common port of the transceiver common mode coupling module A (104). The emitted optical signal is transformed by the convex lens A1 (107) and then incident on the spatial optical phase modulator A (102). The optical signal emitted from the spatial optical phase modulator A (102) is further transformed by the convex lens A2 (108) and then passes through the optical transceiver aperture A (103) to enter the free space optical channel for transmission. After reaching the terminal B, the optical signal enters the optical transceiver aperture B (203) and passes through the convex lens A2 (108). After being transformed by the mirror B2 (208), the optical signal emitted from the spatial optical phase modulator B (202) is incident on the transmitting and receiving common port of the transmitting and receiving common mode coupling module B (204) after being transformed by the convex lens B1 (207). The optical signal emitted from the receiving optical output port of the transmitting and receiving common mode coupling module B (204) is incident on the detector B (205) through the single-mode optical fiber. The electrical signal output by the detector B (205) is transmitted to the acquisition card of the computer B (206) and is sampled and quantized into a digital signal and stored in the computer B (206); The optical signal emitted by the laser B (201) is incident on the transmitting light input port of the transceiver common mode coupling module B (204) through the single-mode optical fiber, and is emitted from the transceiver common port of the transceiver common mode coupling module B (204). The emitted optical signal is transformed by the convex lens B1 (207) and then incident on the spatial optical phase modulator B (202). The optical signal emitted from the spatial optical phase modulator B (202) is further transformed by the convex lens B2 (208) and then passes through the optical transceiver port B (203) to enter the free space optical channel for transmission. After reaching the terminal A, the optical signal enters the optical transceiver port A (103) and passes through the convex lens B1 (207). After being transformed by lens A2 (108), the optical signal emitted from the spatial optical phase modulator A (102) is incident on the transmitting and receiving common port of the transmitting and receiving common mode coupling module A (104) after being transformed by convex lens A1 (107). The optical signal emitted from the receiving optical output port of the transmitting and receiving common mode coupling module A (104) is incident on the detector A (105) through the single-mode optical fiber. The electrical signal output by the detector A (105) is transmitted to the acquisition card of the computer A (106) and is sampled and quantized into a digital signal and stored in the computer A (106); The random phase control signal output by computer B (206) is transmitted to the control port of spatial optical phase modulator B (202) for controlling the spatial phase modulation of the optical signal incident on spatial optical phase modulator B (202); the random phase control signal output by computer A (106) is transmitted to the control port of spatial optical phase modulator A (102) for controlling the spatial phase modulation of the optical signal incident on spatial optical phase modulator A (102).

2. The random phase modulation FSO channel key distribution system according to claim 1, characterized in that: The spatial light phase modulator A (102) and the spatial light phase modulator B (202) both use reflective liquid crystal spatial light modulators.

3. The random phase modulation FSO channel key distribution system according to claim 1, characterized in that: The transceiver common mode coupling module A (104) and the transceiver common mode coupling module B (204) are both implemented using optical fiber circulators.

4. The random phase modulation FSO channel key distribution system according to claim 1, characterized in that: The detector A (105) and the detector B (205) are both PIN photodetectors or APD photodetectors.

5. The random phase modulation FSO channel key distribution system according to claim 1, characterized in that: The computer A (106) and the computer B (206) communicate with each other via the Internet.

6. A random phase modulation FSO channel key distribution method, characterized in that: The applicable system is the random phase modulation FSO channel key distribution system according to any one of claims 1 to 5, comprising the following steps: Step S1, make terminal A and terminal B work normally; Computer A (106) outputs a random phase control signal of spatial optical phase modulator A (102) every time τs starting from time t0, so as to control spatial phase modulation of an incident optical signal generated by spatial optical phase modulator A (102); Computer B (206) outputs a random phase control signal of spatial optical phase modulator B (202) every time τs starting from time t0, so as to control spatial phase modulation of an incident optical signal generated by spatial optical phase modulator B (202); Computer A (106) samples and measures the electrical signal output by detector A (105) once every time τs from time t0 to obtain a sampled measurement value MsA; computer A (106) obtains a total of Nt+1 sampled measurement values ​​MsA at time Nt×τs+t0, where Nt is a positive integer; these Nt+1 sampled measurement values ​​MsA are stored in a list LISTA in a memory of computer A (106) in the order of their acquisition time; the i-th sampled measurement value MsA is obtained at time (i-1)×τs+t0, where i=1, 2, 3, ..., Nt+1; Computer B (206) samples and measures the electrical signal output by detector B (205) once every time τs from time t0 to obtain a sampled measurement value MsB; computer B (206) obtains a total of Nt+1 sampled measurement values ​​MsB at time Nt×τs+t0, where Nt is a positive integer; these Nt+1 sampled measurement values ​​MsB are stored in a list LISTB in a memory of computer B (206) in the order of their acquisition time; and the i-th sampled measurement value MsB is obtained at time (i-1)×τs+t0, where i=1, 2, 3, ..., Nt+1; Step S2: Execute the following steps in computer A (106): Step S201: Treat the values ​​of all elements of the list LISTA as random observations, calculate the corresponding empirical cumulative distribution function FA(x) using a program in computer A (106), and take the value of x that makes FA(x) closest to 0.5 as the decision threshold TxA; create a list KeyLA in the memory of computer A (106), and set the list KeyLA to be empty; Step S202: For i=1, 2, 3, ..., Nt+1, perform the following operations in sequence: Let MsAi represent the value of the i-th element of the list LISTA; if the value of MsAi is greater than the decision threshold TxA, then add an element to the end of the list KeyLA and set the value of the element equal to 1, otherwise add an element to the end of the list KeyLA and set the value of the element equal to 0; Step S3: Execute the following steps in computer B (206): Step S301: Treat the values ​​of all elements of the list LISTB as random observations, calculate the corresponding empirical cumulative distribution function FB(x) using a program in the computer B (206), and use the value of x that makes FB(x) closest to 0.5 as the decision threshold TxB; create a list KeyLB in the memory of the computer B (206), and set the list KeyLB to be empty; Step S302: For i=1, 2, 3, ..., Nt+1, perform the following operations in sequence: Let MsBi represent the value of the i-th element of the list LISTB; if the value of MsBi is greater than the decision threshold TxB, then add an element to the end of the list KeyLB and set the value of the element equal to 1, otherwise add an element to the end of the list KeyLB and set the value of the element equal to 0; Step S4, using error estimation, key negotiation, and error checking techniques in post-quantum key distribution processing to correct inconsistent bits in the bit sequences of the original shared keys stored in the list KeyLA and the list KeyLB, so that computer A (106) and computer B (206) obtain a consistent shared key bit sequence.

7. The random phase modulation FSO channel key distribution method according to claim 6, characterized in that: τs=1 millisecond, Nt=10000.

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