A quantum secure direct communication method based on passive encoding

Abstract

The application discloses a quantum secure direct communication method based on passive coding. An information receiver uses two phase random coherent pulses to generate weak coherent pulses in different quantum states through CPBS beam combination and BS attenuation. The information receiver inputs the state of one port output of the BS into a PBS, measures the light intensity ratio of two output ports of the PBS, obtains the state information of the pulse output from the other port of the BS, and sends the state to be sent to an information sender according to the information. The information sender sends the photon pulse back to the information receiver after coding. The information receiver decodes the information sent by the information sender according to the initial pulse information sent by the information receiver. The method does not need to actively modulate the initial quantum state of the light source, realizes passive coding, simplifies the experimental operation, resists side channel attacks of a third-party eavesdropper on the light source modulator, and enhances the communication security.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of quantum communication, and particularly relates to a quantum secure direct communication method based on passive encoding. BACKGROUND

[0002] Quantum secure direct communication (QSDC) is an important branch of quantum communication. It can directly transmit information between communication parties. In 2000, Long Guilu et al. proposed the first quantum secure direct communication protocol. In 2003, Deng Fuguo et al. proposed a two-step QSDC scheme based on EPR entangled pairs using the idea of dense coding; in 2004, the research group proposed a one-time pad QSDC scheme based on single photons; the one-time pad QSDC scheme based on single photons and the two-step QSDC scheme based on entanglement were experimentally verified in 2016 and 2017, respectively. However, in practical applications, the equipment is not perfect. These imperfect devices may provide opportunities for third-party eavesdroppers, threatening the security of the protocol. In 2020, a measurement-device-independent (MDI) quantum secure direct communication protocol was proposed, which can resist all attacks on the measurement device end. However, the imperfection of the light source end device can also introduce some security vulnerabilities, especially when we actively modulate quantum states, a third-party eavesdropper can steal information through the side channel caused by the imperfection of the source end device. In 2010, M. Curty et al. proposed a passive encoding method. Passive encoding is achieved through phase-random coherent pulses, which can simplify the experimental setup and eliminate the side channel information leakage caused by active operation. The passive encoding method has not been applied to the QSDC protocol. SUMMARY

[0003] The purpose of the present application is to overcome the deficiencies in the prior art, and to provide a quantum secure direct communication method and system based on passive encoding, which can simplify experimental operations, resist side channel attacks on the light source modulator, and improve communication security.

[0004] To achieve the above purpose, the present application adopts the following technical solutions:

[0005] A quantum secure direct communication method based on passive encoding comprises the following steps:

[0006] Step 1: The information receiver prepares two coherent pulses μ1 and μ2 with the same intensity and random phase. The pulses μ1 and μ2 are combined through a circular polarization beam splitter (CPBS) to generate pulse μ 1+2 ; Pulse μ 1+2 is split through a beam splitter (BS) to generate μ m and μ out ; μ m is input into a polarization beam splitter (PBS) to generate μ H, μ V , measured μ H , μ V intensity ratio, to obtain the state information of μ out .

[0007] Step 2: The information receiver repeats the operation of step 1 to generate a series of weak coherent pulses, and the information receiver selects the pulses to be sent according to the measured information and sends them to the information sender.

[0008] Step 3: The information sender stores the received photon pulses. Then the information receiver and the information sender negotiate to select a part of the photons for the first round of security detection. The information receiver publishes the information of the corresponding position photons, and the information sender estimates the error rate according to the information of the information receiver. When the error rate is lower than the threshold, the communication continues.

[0009] Step 4: The information sender randomly selects a part of the remaining photons for random encoding, and the remaining photons are encoded with information. After encoding, they are sent to the information receiver.

[0010] Step 5: The information receiver performs X basis or Z basis measurement on the received photons.

[0011] Step 6: The information sender publishes the position and random encoding information of the randomly encoded photons, and the information receiver compares the measurement results of the corresponding positions to estimate the error rate. When the error rate is lower than the threshold, the communication continues.

[0012] Step 7: The information receiver restores the information of the information sender through classical post-processing according to the measurement information of the other position photons.

[0013] Further, the two coherent pulses μ1, μ2 with the same intensity and random phase in step 1 are expressed as:

[0014]

[0015] where μ represents the intensity of the coherent pulse; φ1, φ2 represent the random phases of the two coherent pulses; i is an imaginary number, i 2 =-1. The subscript represents the quantum state of the photon in the coherent light, where represents that the photon is in the quantum state represents that the photon is in the quantum state where |H> and |V> are the horizontal and vertical polarizations of the photon, respectively.

[0016] Further, the pulse μ 1+2 in step 1 is expressed as:

[0017]

[0018] where the subscript represents the quantum state of the photon in the pulse is:

[0019]

[0020] where θ = φ2- φ1.

[0021] Further, the BS transmittance in step 1 is t, and the reflectance is (1-t). The pulse μ m , μ out generated by the BS is expressed as:

[0022]

[0023]

[0024] Further, the pulse μ H , μ V in step 1 is expressed as:

[0025]

[0026] where the subscript represents the horizontal (vertical) polarization of the photon in the coherent light.

[0027] The ratio of the light intensity is:

[0028]

[0029] Further, the information receiver in step 2 screens the pulse to be sent according to the measured information, specifically, the information receiver obtains the value of θ of the state according to the ratio of the light intensity of μ H , μ V , and when θ is in the following interval, the photon pulse is sent to the information sender.

[0030] θ ∈ (θ x - Δθ, θ x + Δθ)

[0031] where Δθ is selected according to the actual system needs, and the value of θ x is 0, π. At this time, the state sent is denoted as |H>, |V>, |+>, |->.

[0032] Further, the information sender in step 4 encodes and randomly encodes the photon in hand, and the encoding operation is

[0033] U0 = |H><H| + |V><V|, U1 = |V><H| - |H><V|.

[0034] Random encoding Randomly using U0 and U1 encoding, information encoding selects U0 and U1 encoding according to the information to be sent, U0 represents information 0, and U1 represents information 1.

[0035] Further, the information receiver in step 5 performs X basis or Z basis measurement on the received photons, specifically, when the initial state sent by the information receiver is |H> and |V>, he performs Z basis measurement, and when the initial state sent by the information receiver is |+> and |->, he performs X basis measurement.

[0036] The present application has the following beneficial effects:

[0037] 1. The quantum secure direct communication method based on passive encoding provided by the present application does not need external driving elements to modulate quantum states, and for protocols running at high transmission rates, can effectively reduce the experimental complexity.

[0038] 2. The quantum secure direct communication method based on passive encoding provided by the present application does not need to actively modulate quantum states, can resist side channel attacks against light source modulators, improves the security of quantum secure direct communication, and at the same time, the security information capacity is similar to that of active modulation QSDC. DETAILED DESCRIPTION

[0039] Figure 1 is a flowchart of the quantum secure direct communication method provided by the embodiment of the present application;

[0040] Figure 2 is a structural principle block diagram of a quantum secure direct communication system provided by the embodiment of the present application;

[0041] Figure 3 is a structural diagram of a passive encoding light source provided by the embodiment of the present application;

[0042] Figure 4 is a comparison diagram of the quantum secure direct communication method based on passive encoding provided by the embodiment of the present application and the optimal performance of the existing active encoding scheme. DETAILED DESCRIPTION

[0043] The technical solutions of the present application will be further described in detail below in combination with the drawings of the specification. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0044] Embodiment one:

[0045] As shown in the accompanying Figure 1 The quantum secure direct communication implementation scheme of the present embodiment comprises the following steps:

[0046] Step 1: as Figure 3As shown, information receiver Bob prepares two coherent pulses μ1, μ2 with the same intensity and random phase, the coherent pulses μ1, μ2 are combined by CPBS to generate pulse μ 1+2 ; pulse μ 1+2 is split by BS to generate μ m , μ out ; pulse μ m is input into PBS to generate μ H , μ V , the ratio of light intensity of μ H , μ V is measured to obtain the state information of μ out .

[0047] Two coherent pulses μ1, μ2 with the same intensity and random phase are expressed as:

[0048]

[0049] Wherein μ represents the intensity of the coherent pulse; φ1, φ2 represent the random phase of the two coherent pulses; i is an imaginary number, i 2 =-1. Subscript represents the quantum state of the photon in the coherent light, wherein represents that the photon is in quantum state represents that the photon is in quantum state Wherein |H> and |V> are the horizontal and vertical polarizations of the photon respectively.

[0050] The pulse μ 1+2 combined by CPBS is expressed as:

[0051]

[0052] Wherein, subscript represents that the quantum state of the photon in the pulse is:

[0053]

[0054] Wherein θ=φ2-φ1.

[0055] After the information receiver inputs the pulse μ 1+2 into BS with transmittance t and reflectance (1-t), the generated pulses μ m , μ out are expressed as:

[0056]

[0057] After the information receiver inputs the pulse μ m into PBS, the generated pulses μ H , μ VExpressed as:

[0058]

[0059] Wherein the subscript represents the photon level (vertical) polarization in coherent light.

[0060] The ratio of their light intensity is:

[0061]

[0062] The information receiver obtains the value of θ by measurement.

[0063] Step 2: The information receiver repeats the operation of step 1 to generate a series of weakly coherent pulses, and the information receiver selects the pulses to be sent according to the measured information and sends them to the information sender Alice.

[0064] When the measured θ is in the following interval, the photon pulse is sent to the information sender.

[0065] θ∈(θ x -Δθ,θ x +Δθ)

[0066] Wherein Δθ is selected according to the actual system needs, θ x The value of θ At this time, the state sent is denoted as |H>, |V>, |+>, |->.

[0067] Step 3: The information sender stores the received photon pulses. Then the information receiver and the information sender negotiate to select a part of the photons for the first round of security detection. The information receiver publishes the information of the corresponding position photons, and the information sender estimates the bit error rate according to the information of the information receiver. When the bit error rate is lower than the threshold, the communication continues.

[0068] Step 4: The information sender randomly selects a part of the remaining photons for random encoding, and the remaining photons are encoded with information. After encoding, it is sent to the information receiver.

[0069] Wherein the encoding operation is

[0070] U0 = |H><H| + |V><V|, U1 = |V><H| - |H><V|.

[0071] Random encoding randomly uses U0 and U1 encoding, and information encoding selects U0 and U1 encoding according to the information to be sent, U0 represents information 0, and U1 represents information 1.

[0072] Step 5: The information receiver performs X basis or Z basis measurement on the received photons.

[0073] When the initial state |H> and |V> sent by the information receiver, he makes Z basis measurement, when the initial state |+> and |-> sent by the information receiver, he makes X basis measurement.

[0074] Step 6: The information sender publishes the position of the random encoding photon and the random encoding information, the information receiver compares the measurement results of the corresponding position, estimates the error rate, and when the error rate is lower than the threshold, continues the communication.

[0075] Step 7: The information receiver restores the information of the information sender according to the measurement information of the photon of other positions through classical post-processing.

[0076] Figure 4 The figure is the comparison of the optimal performance of the present passive encoding based quantum secure direct communication method and the existing active encoding scheme. The passive encoding based quantum secure direct communication method provided by the present application does not need to actively modulate the quantum state, can resist side channel attacks on the light source modulator, improves the security of the quantum secure direct communication, and is close to the security information capacity of the active modulation QSDC.

[0077] Embodiment two:

[0078] As shown in Figure 2 , the present application further provides a quantum secure direct communication system, comprising an information receiver Bob and an information sender Alice. The communication method is described in Figure 1 . The information receiver sends the quantum state random photon pulse to the information sender through passive encoding. The information sender stores the received photon, and then selects a part of the photon for the first round of security detection. After the security detection, the information sender encodes the information and randomly encodes, and then sends the encoded photon to the information receiver, and the information receiver decodes and performs the second round of security detection. For the specific method steps performed by them, please refer to embodiment one, which will not be repeated here to save space.

[0079] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer usable program code.

[0080] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks. Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks.

[0081] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks. Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks.

[0082] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart Figure 1 one or more functions specified in the flowchart or multiple flows and / or blocks. ​ one or more functions specified in the flowchart or multiple flows and / or blocks.

[0083] The above only is the preferred embodiment of the present application, it should be pointed out that, for those skilled in the technical field, without departing from the technical principles of the present application, can also make a number of improvements and variations, these improvements and variations should also be considered as the protection scope of the present application.

Claims

1. A method for quantum secure direct communication based on passive encoding, characterized in that: The method comprises the following steps: Step 1: the information receiver prepares two coherent pulses μ1, μ2 with the same intensity and random phase, the coherent pulses μ1, μ2 are combined by a circular polarization beam splitter to generate pulse μ 1+2 ; pulse μ 1+2 is split by the beam splitter to generate μ m , μ out ; pulse μ m is input into the polarization beam splitter to generate μ H , μ V , the ratio of the light intensity of μ H , μ V is measured to obtain the state information of μ out ; The two coherent pulses μ1, μ2 with the same intensity and random phase are expressed as: Wherein μ represents the intensity of the coherent pulse; φ1, φ2 represent the random phases of the two coherent pulses; i is the imaginary unit, i 2 = -1 ; the subscript denotes the quantum state in which a photon in coherent light is located, wherein denotes that the photon is in the quantum state denotes that the photon is in the quantum state where |H> and |V> are the horizontal and vertical polarizations of the photon, respectively; Step 2: The information receiver repeats the operation of step 1 to generate a series of weak coherent pulses, and the information receiver selects the pulses to be sent according to the measured information and sends them to the information sender; Specifically, the information receiving party obtains the value of θ according to the ratio of the light intensity H , μ V The value of θ is obtained when θ is in the following interval: the photon pulse is sent to the information sender; θ e (θ x - Δθ, θ x + Δθ) where Δθ is selected according to the actual system requirement, θ x The value of θ is 0, π, At this time, the state sent is |H>, |V>, |+>, |->. Step 3: The information sender stores the received photon pulses, and then the information receiver and the information sender select a part of the photons for the first round of security detection after consultation, the information receiver publishes the information of the corresponding position photons, and the information sender estimates the bit error rate according to the information of the information receiver, when the bit error rate is lower than the threshold, continue communication; Step 4: The information sender randomly selects a part of the remaining photons for random encoding, and the remaining photons are information encoded, and then sent to the information receiver after encoding; Step 5: The information receiver measures the received photons in X basis or Z basis; Step 6: The information sender publishes the position and random encoding information of the random encoding photons, and the information receiver compares the measurement results of the corresponding positions to estimate the bit error rate, and when the bit error rate is lower than the threshold, continue communication; Step 7: The information receiver restores the information of the information sender according to the measurement information of the other position photons through classical post-processing.

2. The method according to claim 1, wherein the method is a passive encoding based quantum secure direct communication method. The pulses μ 1+2 The expression is: where the subscript represents the quantum state of the photon in the pulse is: Wherein θ = φ2-φ1, |vac> represents the vacuum state. 3.The method of claim 1, wherein the method is characterized in that: The beamsplitter described in step 1 has a transmittance t and a reflectance (1-t). The pulses μ generated by the beamsplitter are m , out expressed as:

4. The method according to claim 1, wherein the method is characterized in that: The pulses μ H , μ V are expressed as: where the subscript represents the photon level (vertical) polarization in the coherent light; the ratio of its light intensity is:

5. The method according to claim 1, wherein the method is characterized in that: In step 4, the information sender encodes the photons in hand with information and random encoding, wherein the encoding operation is U0 = |H><H| + |V><V|, U1 = |V><H|-|H><V| Random encoding randomly uses U0 and U1 encoding, and information encoding selects U0 and U1 encoding according to the information to be sent, U0 represents information 0, and U1 represents information 1.

6. The method according to claim 1, wherein the method is characterized in that: In step 5, the information receiver measures the received photons in X basis or Z basis, specifically, when the initial state sent by the information receiver is |H> and |V>, Z basis measurement is performed, and when the initial state sent by the information receiver is |+> and |->, X basis measurement is performed.

7. A quantum secure direct communication system, characterized by, The information sender and the information receiver for executing the communication method of any one of claims 1 to 6.

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