Quantum secure direct communication method based on passive coding

Abstract

The invention discloses a quantum secure direct communication method based on passive coding, and the method comprises the steps: an information receiver uses two coherent pulses with random phases, and randomly generates weak coherent pulses in different quantum states through CPBS beam combination and BS attenuation; and the information receiver inputs the output state of one port of the BS into the PBS, measures the light intensity ratio of the two output ports of the PBS, obtains the state information of the output pulse of the other port of the BS, screens the states to be sent according to the information, and sends the states to the information sender. And the information sender sends the photon pulse to the information receiver after coding. And the information receiver decodes according to the pulse information initially sent by the information receiver and restores the information sent by the information sender. According to the method, the initial quantum state of the light source does not need to be actively modulated, passive coding is achieved, experimental operation is simplified, side channel attack of a third-party eavesdropper on the light source modulator is resisted, and communication safety is enhanced.

Description

Technical Field

[0001] The present invention belongs to the field of quantum communication, and in particular relates to a quantum secure direct communication method based on passive coding. Background Art

[0002] Quantum secure direct communication (QSDC) is an important branch of quantum communication. It can directly and securely transmit information between the communicating 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 team 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 defective devices may give third-party eavesdroppers an opportunity to take advantage of and threaten the security of the protocol. In 2020, the measurement device-independent (MDI) quantum secure direct communication protocol was proposed, which can resist all attacks on the measurement device side. However, the imperfection of the light source end device will also introduce some security vulnerabilities, especially when we actively modulate the quantum state, third-party eavesdroppers can steal information through the side channel caused by the imperfect device on the source end. In 2010, M. Curty et al. proposed a passive coding method. Passive coding is achieved through phase-random coherent pulses, which can simplify the experimental setup and eliminate the side channel information leakage caused by active operation. Currently, the passive coding method has not been applied to the QSDC protocol. Summary of the invention

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

[0004] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

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

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

[0007] Step 2: The information receiver repeats the operation of step 1 to generate a series of weakly coherent pulses. The information receiver selects the pulses it wants to send based on 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 discuss and select a portion of photons for the first round of security testing. The information receiver publishes the information of the photons at the corresponding position, and the information sender estimates the bit error rate based on the information of the information receiver. When the bit error rate is lower than the threshold, communication continues.

[0009] Step 4: The information sender randomly selects a portion of the remaining photons for random encoding, and encodes the remaining photons for information. After encoding, it is 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 coding information of the randomly coded photons. The information receiver compares the measurement results of the corresponding positions and estimates the bit error rate. When the bit error rate is lower than the threshold, communication continues.

[0012] Step 7: The information receiver restores the information of the sender through classical post-processing based on the measurement information of photons at other locations.

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

[0014]

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

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

[0017]

[0018] Among them, the subscript The quantum state of the photon in the pulse is:

[0019]

[0020] Where θ = φ2-φ1.

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

[0022]

[0023]

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

[0025]

[0026] The subscript Indicates the horizontal (vertical) polarization of photons in coherent light.

[0027] The ratio of their light intensities is:

[0028]

[0029] Furthermore, the information receiver in step 2 selects the pulses to be sent according to the measured information. Specifically, the information receiver selects the pulses to be sent according to μ H , μ V The ratio of light intensity is used to obtain the θ value of the state. When θ is in the following range, a 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, θ x The values ​​of are 0, π, The states sent at this time are recorded as |H>,|V>,|+>,|->.

[0032] Furthermore, the information sender in step 4 performs information encoding and random encoding on the photons in hand, wherein the encoding operation is

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

[0034] Random coding randomly uses U0 and U1 coding, and information coding selects U0 and U1 coding according to the information to be sent. U0 represents information 0 and U1 represents information 1.

[0035] Furthermore, the information receiver described 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 invention has the following beneficial effects:

[0037] 1. The quantum secure direct communication method based on passive coding proposed in the present invention does not require external driving elements to modulate the quantum state, and can effectively reduce the experimental complexity for protocols running at high transmission rates.

[0038] 2. The quantum secure direct communication method based on passive coding proposed in the present invention does not require active modulation of quantum states, can resist side channel attacks on light source modulators, and improves the security of quantum secure direct communication. At the same time, its security information capacity is similar to that of actively modulated QSDC. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of a quantum secure direct communication method provided by an embodiment of the present invention;

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

[0041] Figure 3 is a structural diagram of a passive coded light source provided by an embodiment of the present invention;

[0042] Figure 4 It is a comparison chart of the optimal performance of the quantum secure direct communication method based on passive coding provided by an embodiment of the present invention and the existing active coding scheme. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings of the specification. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0044] Embodiment 1:

[0045] As attached Figure 1 As shown, the quantum secure direct communication implementation scheme of this embodiment includes the following steps:

[0046] Step 1: Figure 3As shown in the figure, the information receiver Bob prepares two coherent pulses μ1 and μ2 with the same intensity and random phase. The coherent pulses μ1 and μ2 are combined through CPBS to generate a pulse μ 1+2 ; The pulse μ 1+2 Through BS splitting, μ m , μ out ; μ m Input PBS to generate μ H , μ V , measure μ H , μ V The ratio of light intensity is obtained. out status information.

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

[0048]

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

[0050] The pulse μ after CPBS combination 1+2 It is expressed as:

[0051]

[0052] Among them, the subscript The quantum state of the photon in the pulse is:

[0053]

[0054] Where θ = φ2-φ1.

[0055] The receiver of the information will pulse μ 1+2 After inputting a BS with a transmittance of t and a reflectivity of (1-t), the generated pulse μ m , μ out It is expressed as:

[0056]

[0057] The receiver of the information will pulse μ m Input PBS, the generated pulse μ H , μ VIt is expressed as:

[0058]

[0059] The subscript Indicates the horizontal (vertical) polarization of photons in coherent light.

[0060] The ratio of their light intensities is:

[0061]

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

[0063] Step 2: The information receiver repeats the operation of step 1 to generate a series of weakly coherent pulses. The information receiver selects the pulses it wants to send based on the measured information and sends them to the information sender Alice.

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

[0065] θ∈(θ x -Δθ,θ x +Δθ)

[0066] Where Δθ is selected according to the actual system needs, θ x The values ​​of are 0, π, The states sent at this time are recorded as |H>,|V>,|+>,|->.

[0067] Step 3: The information sender stores the received photon pulses. Then the information receiver and the information sender discuss and select a portion of photons for the first round of security testing. The information receiver publishes the information of the photons at the corresponding position, and the information sender estimates the bit error rate based on the information of the information receiver. When the bit error rate is lower than the threshold, communication continues.

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

[0069] The encoding operation is

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

[0071] Random coding randomly uses U0 and U1 coding, and information coding selects U0 and U1 coding 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 information receiver sends the initial states |H> and |V>, he performs Z-basis measurement. When the information receiver sends the initial states |+> and |->, he performs X-basis measurement.

[0074] Step 6: The information sender publishes the position and random coding information of the randomly coded photons. The information receiver compares the measurement results of the corresponding positions and estimates the bit error rate. When the bit error rate is lower than the threshold, communication continues.

[0075] Step 7: The information receiver restores the information of the sender through classical post-processing based on the measurement information of photons at other locations.

[0076] Figure 4 This is a comparison chart of the optimal performance of the quantum secure direct communication method based on passive coding provided by the present invention and the existing active coding scheme. The quantum secure direct communication method based on passive coding proposed by the present invention does not require active modulation of quantum states, can resist side channel attacks on light source modulators, improves the security of quantum secure direct communication, and its security information capacity is similar to that of actively modulated QSDC.

[0077] Embodiment 2:

[0078] like Figure 2 As shown, the embodiment of the present invention also provides a quantum secure direct communication system, including an information receiver Bob and an information sender Alice. The communication method thereof is shown in Figure 1 . The information receiver prepares quantum state random photon pulses through passive encoding and sends them to the information sender. The information sender stores the received photons and then selects a portion of the photons for the first round of security testing. After the security test is passed, the information sender performs information encoding and random encoding, and then sends the encoded photons to the information receiver, who performs decoding and the second round of security testing. For the specific method steps they perform, please refer to Example 1. In order to save space, they will not be repeated here.

[0079] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0080] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0081] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0082] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A quantum secure direct communication method based on passive coding, characterized in that: The method comprises the following steps: Step 1: The information receiver prepares two coherent pulses μ1 and μ2 with the same intensity and random phase. The coherent pulses μ1 and μ2 are combined through a circular polarization beam splitter to generate a pulse μ 1+2 ; The pulse μ 1+2 The beam is split by a beam splitter to generate μ m , μ out ; m Input polarization beam splitter to generate μ H , μ V , measure μ H , μ V The ratio of light intensity is obtained. out Status information; Step 2: The information receiver repeats the operation of step 1 to generate a series of weakly coherent pulses. The information receiver selects the pulses to be sent based on the measured information and sends them to the information sender. Step 3: The information sender stores the received photon pulses, and then the information receiver and the information sender discuss and select a part of the photons for the first round of security detection. The information receiver publishes the information of the photons at the corresponding position. The information sender estimates the bit error rate based on the information of the information receiver. When the bit error rate is lower than the threshold, the communication continues; Step 4: The information sender randomly selects a portion of the remaining photons for random encoding, and encodes the remaining photons for information, and after encoding, sends them to the information receiver; Step 5: The information receiver performs X-based or Z-based measurement on the received photons; Step 6: The information sender publishes the position and random coding information of the randomly coded photons. The information receiver compares the measurement results of the corresponding positions and estimates the bit error rate. When the bit error rate is lower than the threshold, the communication continues. Step 7: The information receiver restores the information of the sender through classical post-processing based on the measurement information of photons at other locations.

2. According to claim 1, a quantum secure direct communication method based on passive coding is characterized in that: The two coherent pulses μ1 and μ2 with the same intensity and random phase described in step 1 are expressed as: Where μ represents the intensity of the coherent pulse; φ1 and φ2 represent the random phases of the two coherent pulses; i is an imaginary number, i 2 =-1; subscript represents the quantum state of the photons in the coherent light, where Indicates that the photon is in a quantum state Indicates that the photon is in a quantum state where |H> and |V> are the horizontal and vertical polarizations of the photon, respectively.

3. According to claim 1, a quantum secure direct communication method based on passive coding is characterized in that: The pulse μ described in step 1 1+2 It is expressed as: Among them, the subscript The quantum state of the photon in the pulse is: Where θ=φ2-φ1, |vac> represents the vacuum state.

4. According to claim 1, a quantum secure direct communication method based on passive coding is characterized in that: The transmittance of the beam splitter described in step 1 is t, the reflectivity is (1-t), and the pulse μ generated by the beam splitter is m , μ out It is expressed as:

5. According to claim 1, a quantum secure direct communication method based on passive coding is characterized in that: The pulse μ described in step 1 H , μ V It is expressed as: The subscript Indicates the horizontal (vertical) polarization of photons in coherent light; the ratio of their light intensities is:

6. The quantum secure direct communication method based on passive coding according to claim 1, characterized in that: The information receiver in step 2 selects the pulses to be sent according to the measured information. Specifically, the information receiver selects the pulses to be sent according to μ H , μ V The ratio of light intensity is used to obtain the θ value of the state. When θ is in the following interval, a photon pulse is sent to the information sender; θ∈(θ x -Δθ,θ x +Δθ) Where Δθ is selected according to the actual system needs, θ x The values ​​of are 0, π, The states sent at this time are recorded as |H>, |V>, |+>, |->.

7. The quantum secure direct communication method based on passive coding according to claim 1, characterized in that: The information sender in step 4 performs information encoding and random encoding on the photons in his hand, where the encoding operation is U0=|H> <H|+|V><V|,U1=|V><H|-|H><V| Random coding randomly uses U0 and U1 coding, and information coding selects U0 and U1 coding according to the information to be sent. U0 represents information 0 and U1 represents information 1.

8. The quantum secure direct communication method based on passive coding according to claim 1, characterized in that: The information receiver described in step 5 performs X-based or Z-based measurement on the received photons. Specifically, when the initial state sent by the information receiver is |H> and |V>, Z-based measurement is performed, and when the initial state sent by the information receiver is |+> and |->, X-based measurement is performed.

9. A quantum secure direct communication system, characterized in that: It includes an information sender and an information receiver for executing the communication method described in any one of claims 1 to 8.

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