CN117097475A - Security analysis system and method based on four-state quantum communication - Google Patents
Security analysis system and method based on four-state quantum communication Download PDFInfo
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Abstract
The invention discloses a security analysis system and method based on four-state quantum communication. The method comprises the following steps: the transmitting end randomly prepares one of four quantum states, codes in single photon pulse and transmits the single photon pulse to the receiving end through a quantum channel; the receiving end randomly selects Z base or X base for measurement and publishes X base pulse information through a classical channel; and the transmitting end calculates a safe intermediate parameter C by an analytic statistics method according to the published information and combining the corresponding preparation quantum state, thereby obtaining the maximum mutual information quantity of the tightening quantum channel. The system comprises a light source, a coding and decoding module, a quantum channel and a single photon detector. The technical scheme provided by the invention not only avoids using high-consumption system resources, but also improves the quantum key generation rate, thereby being beneficial to realizing the commercial application of four-state reference system independent quantum communication.
Description
Technical Field
The invention relates to the field of quantum secret communication, in particular to a security analysis system and method based on four-state quantum communication.
Background
In quantum communications, the communication system reference frame is subject to real-time rotational variations due to environmental noise, and in order to avoid real-time calibration operation of the reference frame, an Anthony Lang in 2010 proposed a reference-frame independent quantum key distribution protocol (Reference Frame Independent Quantum Key Distribution, RFI-QKD). In this protocol, the communicating parties may be protected from slowly varying reference frame drift, ultimately producing a security key. The RFI-QKD protocol is similar to the traditional six-state protocol, and requires the use of three sets of bases for encoding and decoding, namely, a Z base, an X base and a Y base. The sender Alice and the receiver Bob only need to align one group of bases, and the other two groups of bases can change slowly during communication without affecting the generation of the security key. However, in communication, the sender Alice needs to send six quantum states of Z, X, Y under three bases, Z0, Z1, X0, X1, Y0 and Y1, respectively, and the receiver Bob also needs to make Z, X, Y measurements under three bases. Compared with the traditional BB84 QKD protocol, the RFI-QKD protocol has the advantages that the implementation difficulty of the protocol is greatly increased due to the new requirements on the complexity of equipment, and the commercial application is very difficult.
In order to reduce the difficulty of quantum state preparation, in 2019 Liu et al, proposed a four-state RFI-QKD protocol, that is, a sender Alice only needs to prepare four quantum states of Z0, Z1, X0 and Y0, but in this protocol, the difficulty of measurement of a receiver Bob is not reduced, and measurement still needs to be performed under Z, X, Y three bases. Norbert et al, the same year, proposed a 6-4 state QKD protocol in which the sender Alice randomly prepares six quantum states, and the receiver Bob only uses Z-based and X-based measurements. The QKD protocol described above reduces the key preparation difficulty to some extent, but does not reduce both the preparation difficulty of the sender and the measurement difficulty of the receiver.
In the prior art, chinese patent CN 115208568B proposes a new four-state RFI-QKD protocol, in which sender Alice only needs to prepare four quantum states of Z0, Z1, X0 and Y0, while receiver Bob only needs to perform in two measurement bases Z and X. The novel four-state RFI-QKD protocol not only reduces the quantum state preparation quantity, but also reduces the complexity of quantum channel security estimation to a certain extent by reducing the measurement basis quantity. However, according to the traditional channel security analysis method, the RFI-QKD protocol of the Chinese patent can obtain the phase error rate by solving a series of optimization equations, and finally, the unconditionally secure quantum key is prepared by calculating the maximum mutual information quantity of the eavesdropper Eve. Because solving the optimization equation not only requires the data processing hardware FPGA of the system to have extremely high performance parameters, but also requires ARM soft core cooperation calculation, system resources are seriously consumed, and the complexity and cost of equipment are prevented from being reduced. Therefore, the traditional security analysis method is unfavorable for the popularization and application of the new four-state RFI-QKD protocol in commerce.
Disclosure of Invention
Based on the above, in order to overcome the defects, the technical scheme of the invention adopts a statistical solution method to calculate the intermediate parameter C of the four-state RFI-QKD, and can directly obtain the maximum mutual information quantity compact by the eavesdropping end.
The invention aims at realizing the following technical scheme: a security analysis method based on four-state quantum communication is characterized in that the method comprises the following steps of,
the method comprises the steps that a sending end prepares single photon pulses, and the single photon pulses are sent to a receiving end through a quantum channel; the single photon pulse comprises a single photon; the first quantum state of the single photon is randomly selected from four quantum states by the transmitting end to prepare; the four quantum states are Z0 state, Z1 state, X0 state and Y0 state respectively; the Z0 state and the Z1 state are quantum states prepared under a Z base, the X0 state is a quantum state prepared under an X base, and the Y0 state is a quantum state prepared under a Y base;
the receiving end randomly selects the Z base or the X base to measure the single photon, and a second quantum state of the single photon is obtained;
the receiving end publishes sequence information of all X-based pulses through a classical channel, and the second quantum state of the single photon in the X-based pulses; the X-based pulse is a single photon pulse measured by the receiving end by using the X-based pulse;
the transmitting end extracts the first quantum state of the single photon according to the sequence information of the X-based pulse, calculates the maximum mutual information quantity of the eavesdropping end on the quantum channel by combining the second quantum state statistical intermediate parameter C of the single photon,
，
wherein,is a binary shannon entropy function.
Further, the intermediate parameter C is calculated according to the following formula:
，
wherein,representing the first quantum state as +.>The second quantum state is +.>Is provided for the single photon pulse.
Preferably, the security analysis method further comprises,
correcting the intermediate parameter C by using the statistical fluctuation characteristic of the limited data,
，
wherein,is the accuracy of the minimum smoothed entropy estimate, +.>。
Preferably, the security analysis method further comprises:
the receiving end publishes sequence information of part of Z-based pulses through a classical channel, and the second quantum state of the single photon in the part of Z-based pulses; the Z-based pulse is the single photon pulse measured by the receiving end by using the Z-based pulse;
and the transmitting end extracts the first quantum state of the single photon according to the partial Z-based pulse and calculates the key length by adopting a statistical average method.
Further, the method also comprises the step of acquiring the counting quantity and the error rate by adopting a decoy state method.
The technical scheme of the invention also provides a security analysis system based on four-state quantum communication, which adopts the security analysis method to carry out security analysis of the quantum channel, and comprises the following steps:
the transmitting end comprises a light source and a coding module; the light source is a single photon source and is used for generating single photon pulses, and the coding module is used for randomly selecting and coding four quantum states on single photons of the single photon pulses to prepare first quantum states of the single photons; the four quantum states are Z0 state, Z1 state, X0 state and Y0 state respectively; the Z0 state and the Z1 state are quantum states prepared under a Z base, the X0 state is a quantum state prepared under an X base, and the Y0 state is a quantum state prepared under a Y base;
the receiving end comprises a decoding module and a single photon detector; the decoding module is used for decoding the single photon by selecting a Z base or an X base, outputting the single photon to the single photon detector and obtaining a second quantum state of the single photon;
the quantum channel is arranged between the sending end and the receiving end and is used for transmitting the single photon pulse;
classical channel, set up between stated sender and stated receiving end, used for transmitting the public information.
Specifically, the encoding module comprises a first beam splitter, a first interference ring and a first beam combiner, wherein the first interference ring comprises a first arm and a second arm, and the length of the first arm is greater than that of the second arm;
the first beam splitter is used for splitting the single photon pulse so as to transmit the single photon pulse to the first beam combiner through the first arm and the second arm respectively; the first arm is provided with a first optical attenuator, and the second arm is provided with a second optical attenuator; when the first optical attenuator or the second optical attenuator is in a closed state, the first beam combiner outputs the quantum state under the Z base to the quantum channel.
Further, the encoding module further comprises a first phase modulator arranged on the first arm for generating different phase differences between the single photon pulse passing through the first arm and the single photon pulse passing through the second arm; when the first optical attenuator and the second optical attenuator are in the closed state, the different phase differences enable the first beam combiner to output the quantum state under the X base and the quantum state under the Y base respectively.
Specifically, the decoding module comprises a second beam splitter, a second interference ring and a second beam combiner, wherein the second interference ring comprises a third arm and a fourth arm, and the length of the third arm is greater than that of the fourth arm;
the second beam splitter is used for transmitting the single photon pulse output by the quantum channel to the second beam combiner through the third arm and the fourth arm respectively; the third arm is provided with a third optical attenuator and a second phase modulator, and the fourth arm is provided with a fourth optical attenuator; the second beam combiner is connected with two single photon detectors;
when the third optical attenuator or the fourth optical attenuator is in a closed state, the quantum states detected by the two single photon detectors are quantum states under the Z base;
when the third optical attenuator and the fourth optical attenuator are in the closed state, the quantum states detected by the two single photon detectors are the quantum states under the X base.
From the above, the technical scheme provided by the invention has the following beneficial effects:
1) The intermediate parameter C of the four-state RFI-QKD is calculated by a statistical solution method, so that the computational power resource is saved, the complexity of equipment is controlled, the quantum communication efficiency is improved, and the system cost is reduced;
2) The statistical solution method can obtain the lower limit of the intermediate parameter C, so that the compact upper limit of the mutual information quantity of the eavesdropping terminal is obtained, and the system safety is improved;
3) In the calculation process of the intermediate parameter C, the receiving end uses all single photon pulse results of X-base measurement to participate in calculation, so the technical scheme of the invention has the robustness of limited code length statistical fluctuation.
Drawings
FIG. 1 is a flow chart of calculating mutual information quantity of eavesdropping terminals according to an embodiment of the invention;
FIG. 2 is a schematic diagram of a security analysis system according to an embodiment of the present invention;
FIG. 3 is a key rate of low detection efficiency calculated by simulation in accordance with an embodiment of the present invention;
FIG. 4 is a key rate with high detection efficiency calculated by simulation in accordance with an embodiment of the present invention;
reference numerals illustrate:
1. a light source; 2. A coding module; 3. A decoding module; 4. A single photon detector; 5. a quantum channel; 21. A first beam splitter; 22. A first beam combiner; 23. A first arm; 24. A second arm; 25. A first optical attenuator; 26. A second optical attenuator; 27. A first phase modulator; 31. a second beam combiner; 32. A second beam splitter; 33. A third arm; 34. A fourth arm; 35. A third optical attenuator; 36. A fourth optical attenuator; 37. A second phase modulator.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following detailed description of the present invention will be made with reference to examples. It should be understood that the examples described herein are for illustrative purposes only and are not intended to limit the scope of the present invention.
Example 1
Referring to fig. 1, it can be seen that the embodiment of the invention provides a method for security analysis based on four-state quantum communication, which comprises the following specific steps:
the transmitting end prepares single photon pulse and transmits the single photon pulse to the receiving end through a quantum channel. The single photon pulse comprises one single photon. The first quantum state of the single photon is randomly selected from four quantum states by a transmitting end to prepare; the four quantum states are Z0 state, Z1 state, X0 state and Y0 state respectively. The Z0 state and the Z1 state are quantum states prepared under the Z base, the X0 state is a quantum state prepared under the X base, and the Y0 state is a quantum state prepared under the Y base.
The receiving end randomly selects Z base or X base to measure single photon to obtain a second quantum state.
The receiving end publishes the sequence information of all single photon pulses measured by using an X base through a classical channel, namely X base pulses, and publishes the second quantum state of single photons in the X base pulses.
The transmitting end extracts the first quantum state corresponding to the single photon according to the sequence information of the published X-based pulse, calculates the intermediate parameter C by combining the published second quantum state statistics, calculates the maximum mutual information quantity of the eavesdropping end on the quantum channel by adopting a binary shannon entropy function,
，
wherein,is a binary shannon entropy function.
In particular, for the RFI-QKD of the embodiment of the invention, the quantum state space used by the transmitting end and the receiving end in preparation and measurement is two-dimensional, so that the measurement of the X base and the Y base can be represented by using Pauli operator. In particular, under the Z-based representation, the Z-base, X-base and Y-base can each be represented as:
，
the four quantum states are respectively expressed as:
，
thus, it is possible to obtain:
。
in addition, according to the definition of the intermediate parameter C, it is possible to obtain:
，
if defined:
，
，
then there are:
，
wherein,representing the first quantum state as +.>The second quantum state is->Is provided for the total number of single photon pulses.
Considering the statistical fluctuation of the limited data, the intermediate parameter C can be modified as follows:
，
wherein,is the accuracy of the minimum smoothed entropy estimate, +.>。
Practical quantum communication security analysis systems generally use weak coherent light instead of a single photon source, and thus generally require a decoy-state approach to perform security analysis. Based on the most typical "weak+vacuum" decoy state method, it is assumed that the intensities of the "signal light", "decoy light" and "vacuum light" adopted by the transmitting end are respectively、/>And->And->，/>Therefore, when both the transmitting end and the receiving end adopt the Z-base, the actual count of the vacuum state can be expressed as:
，
wherein,indicating the lower count limit of vacuum light when both the transmitting end and the receiving end use the Z-base. />The upper limit of the count of the decoy state when the sending end and the receiving end adopt the Z base is indicated;
，
representing the probability that the transmitting end transmits the k state. Considering statistical rises and falls, the upper and lower count limits for the k state can be calculated as follows:
，
the count of signal light can be expressed as:
；
the bit error rate of the signal light can be expressed as:
，
wherein,the upper and lower limits are calculated as follows:
。
the security analysis is performed under the condition that the code length is assumed to be infinitely long, and when the influence of the finite code length is considered, the security analysis of the four-state quantum communication in the technical scheme also comprises the calculation of the key length. The receiving end publishes the pulse information of the Z base through a classical channel and corresponds to a second quantum state of the single photon.
After obtaining the mutual information quantity of the eavesdropping terminal according to the first embodiment, the transmitting terminal extracts the first quantum state corresponding to the single photon according to the published sequence information of the part Z base, and calculates the key length by adopting a statistical average method, wherein the specific calculation is as follows:
，
wherein,representing the count of quantum states prepared by the sending end according to the Z-based published pulse information, wherein the quantum states extracted by the sending end are Z-based;
in the counting, the receiving end detects the counting of the empty pulse;
in counting, the receiving end detects the counting of single photon pulses;
bit error rate in count;
for error correction efficiency, the value is between 1.05 and 1.2;
error probability for the error correction step;
error probability for the privacy amplification step;
the minimum smooth entropy precision can be set according to actual application requirements;
is the total count of pulses of the pulse train.
Example two
Referring to fig. 2, a schematic structural diagram of a security analysis system according to an embodiment of the invention is shown. As can be seen from the figure, the security analysis system based on four-state quantum communication performs security analysis on a four-state quantum channel by adopting the security analysis method according to the first embodiment of the present invention, and the security system includes:
the transmitting end comprises a light source 1 and a coding module 2; the light source 1 is a single photon source and is used for generating single photon pulses, and the coding module 2 is used for randomly selecting and coding four quantum states on single photons of the single photon pulses to prepare a first quantum state of the single photons; the four quantum states are Z0 state, Z1 state, X0 state and Y0 state respectively; the Z0 state and the Z1 state are quantum states prepared under the Z base, the X0 state is a quantum state prepared under the X base, and the Y0 state is a quantum state prepared under the Y base.
The existing single photon source is generally generated by means of single atoms, single molecules, diamond color centers, semiconductor quantum dots, nano carbon tubes and the like. There is also a marked single photon source that approximates an ideal single photon source that is created using a nonlinear optical process of photon pairs, such as a parametric down-conversion process or a four-wave mixing process. The number of photons produced by these processes satisfies the cypress distribution.
The encoding module 2 encodes information on physical quantities such as polarization, phase, path, orbital angular momentum of the single photons. In the embodiment of the invention, the encoding module 2 encodes information on the phase of single photons, and common phase encoding is adopted.
The receiving end comprises a decoding module 3 and a single photon detector 4; the decoding module 3 is configured to select a Z group or an X group to decode a single photon, and output the single photon to the single photon detector 4 to obtain a second quantum state of the single photon. In the embodiment of the invention, the single photon detector 4 adopts an InGaAs/InP semiconductor avalanche diode with the response range of 1100nm-1700 nm. In other embodiments, a superconducting nanowire single photon detector, or a silicon single photon detector, may also be selected.
And the quantum channel 5 is arranged between the sending end and the receiving end and is used for transmitting single photon pulses, and the quantum channel 5 comprises a fiber channel or a free space channel. The embodiment of the invention adopts the optical fiber channel, and adopts the commercial single-mode optical fiber with the central wave band of 1550nm and the attenuation coefficient of 0.2 dB/km.
Classical channel, set up between stated sender and stated receiving end, used for transmitting the public information. Classical channel and quantum channel 5 are independent of each other and do not interfere with each other. In the embodiment of the invention, the classical channel adopts common communication transmission.
The encoding module 2 comprises a first beam splitter 21, a first interference ring comprising a first arm 23 and a second arm 24, the lengths of the first arm 23 and the second arm 24 being unequal, and a first beam combiner 22. In the embodiment of the present invention, the length of the first arm 23 is greater than the length of the second arm 24, and in other embodiments, the length of the first arm 23 may be less than the length of the second arm 24.
The first beam splitter 21 is used for splitting the single photon pulse so as to transmit the single photon pulse to the first beam combiner 22 through the first arm 23 and the second arm 24 respectively; the first arm 23 is provided with a first optical attenuator 25 and the second arm 24 is provided with a second optical attenuator 26; when the first optical attenuator 25 or the second optical attenuator 26 is in the off state, the quantum state output by the first beam combiner 22 is the quantum state under the Z-base.
The encoding module 2 further comprises a first phase modulator 27, which first phase modulator 27 is arranged on the first arm 23 in the present embodiment, and which first phase modulator 27 may be arranged on the second arm 24 in other embodiments. The first phase modulator 27 is configured to generate different values of the phase difference between the single photon pulse passing through the first arm 23 and the single photon pulse passing through the second arm 24; when the first optical attenuator 25 and the second optical attenuator 26 are both in the off state, the phase differences of different values between the two arms correspond to the quantum states output by the first beam combiner 22 being respectively the quantum states under the X-base or the quantum states under the Y-base.
The decoding module 3 comprises a second beam splitter 32, a second interference ring comprising a third arm 33 and a fourth arm 34, the lengths of the third arm 33 and the fourth arm 34 being unequal, and a second beam combiner 31. In the embodiment of the present invention, the length of the third arm 33 is longer than the length of the fourth arm 34.
The second beam splitter 32 is configured to transmit the single photon pulses output by the quantum channel to the second beam combiner 31 through the third arm 33 and the fourth arm 34, respectively; the third arm 33 is provided with a third optical attenuator 35 and a second phase modulator 37, and the fourth arm 34 is provided with a fourth optical attenuator 36; the second beam combiner 31 connects the two single photon detectors 4. In other embodiments of the invention, the second phase modulator 37 may also be arranged on the fourth arm 34.
When the third optical attenuator 35 or the fourth optical attenuator 36 is in the off state, the quantum states detected by the two single photon detectors 4 are quantum states under the Z-base;
when both the third optical attenuator 35 and the fourth optical attenuator 36 are in the off state, the quantum states detected by the two single photon detectors 4 are the quantum states under the X-base.
In the encoding module 2, if the X-base or the Y-base is selected, the first optical attenuator 25 and the second optical attenuator 26 provided on the first interference ring are turned off at the same time, the single photon pulse is passed, and the first phase modulator 27 is adjusted. When the phase of the first phase modulator 27 isAt the time of the firstA combiner 22 outputs the quantum state under X; when the phase of the first phase modulator 27 isThe first beam combiner 22 outputs a quantum state at the Y-base. Similarly, the two optical attenuators (the third optical attenuator 35 and the fourth optical attenuator 36) of the decoding module 3 at the receiving end also need to be turned off simultaneously, and the phase difference of the second phase modulator 37 is adjusted to perform the X-base measurement.
Wherein the phase modulator is usually selected fromAn electro-optic modulator of a crystal. The single photon pulse passes through the first interference loop to produce two sub-pulses, and then passes through the quantum channel 5 and the second interference loop, and then there are typically three light pulses of different arrival times. In the embodiment of the invention, the first light pulse is reached through the second arm 24 and the fourth arm 34, the last light pulse is reached through the first arm 23 and the third arm 33, and the light pulse is reached through the first arm 23 and the fourth arm 34, or through the second arm 24 and the third arm 33 at the middle moment.
Example III
In the quantum communication process, both communication parties can obtain all parameters required by a key rate formula through experimental test results. However, for simulation, it is necessary to estimate the count rate and bit error rate of the receiving end under different measurement conditions after passing through different transmission distances. When there is no eavesdropping end, its count rate can be written as:
，
wherein the method comprises the steps of，/>。/>Is the dark count probability of a single photon detector;is the transmission rate of photons transmitted in an L km fiber; />Representing the sending of the quantum state by the sender>When the receiving end detects the quantum state +.>Theoretical probability of (e.g.)>And->. Thus, the counts in the different cases are:
。
in particular, the error rate of the system is mainly composed of two parts:
1) Inherent error rate due to optical system imperfections；
2) The intrinsic measurement error rate of the quantum state, such as transmitting a bit in the Z0 state of 0, but Bob has an intrinsic bit error of 0.5 using the X-base measurement.
Thus, the bit error rate of the system as a whole can be expressed as:
。
and carrying out simulation by taking the formula into a key rate formula. FIGS. 3 and 4 show Key Rate (Key Rate) of a conventional APD single photon detector (20% detection efficiency) and a superconducting single photon detector (90% detection efficiency), respectively, for different Channel losses (Loss of Channel). As can be seen from the figure, the total data length of the quantum channel tolerable loss exceeding 35dB is as follows by adopting a common APD single photon detector. For a 100M repetition frequency system, the corresponding sampling time is about 100s. For GHz systems, the sampling time is about 10s. With superconducting single photon detector, total data length is +.>For a 100M repetition frequency system, the sampling time is about 10s, while for a GHz system, the sampling time is about 1s. Conclusion: it can be seen that the technical scheme provided by the invention can be used for quantum communication irrelevant to a long-distance reference system.
The above simulation is based on the following parameter settings: assuming that the transmitting end transmits four quantum states with equal probability, the receiving end selects Z base or X base with equal probability to carry out base measurement, namely，/>The method comprises the steps of carrying out a first treatment on the surface of the Dark count for single photon detector is +.>Every pulse; the signal state, the decoy state and the vacuum state have the intensities of 0.5,0.1 and 0.01 respectively, and the sending proportion is 0.5,0.4 and 0.1 respectively; the inherent error rate of the optical system is 2%, the error correction and information coordination efficiency is 1.05, and the safety parameter is +.>。
The foregoing is a further detailed description of the invention in connection with specific preferred embodiments, and is not to be construed as limiting the practice of the invention. It should be understood by those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the present invention, and the present invention is not limited to the above-described embodiments.
Claims (9)
1. A security analysis method based on four-state quantum communication is characterized by comprising the following steps:
the method comprises the steps that a sending end prepares single photon pulses, and the single photon pulses are sent to a receiving end through a quantum channel; the single photon pulse comprises a single photon; the first quantum state of the single photon is randomly selected from four quantum states by the transmitting end to prepare; the four quantum states are Z0 state, Z1 state, X0 state and Y0 state respectively; the Z0 state and the Z1 state are quantum states prepared under a Z base, the X0 state is a quantum state prepared under an X base, and the Y0 state is a quantum state prepared under a Y base;
the receiving end randomly selects Z base or X base to measure the single photon, and a second quantum state of the single photon is obtained;
the receiving end publishes sequence information of all X-based pulses through a classical channel, and the second quantum state of the single photon in the X-based pulses; the X-based pulse is a single photon pulse measured by the receiving end by using the X-based pulse;
the sending end extracts the first quantum state of the single photon according to the sequence information of the X-based pulse, calculates the maximum mutual information quantity of the eavesdropping end on the quantum channel by combining the second quantum state statistical intermediate parameter C of the single photon:
，
wherein,is a binary shannon entropy function.
2. The security analysis method according to claim 1, wherein the intermediate parameter C is calculated according to the following formula:
，
wherein,representing the first quantum state as +.>The second quantum state is +.>Is provided for the single photon pulse.
3. The security analysis method according to claim 2, further comprising,
correcting the intermediate parameter C by using the statistical fluctuation characteristic of the limited data,
，
wherein,is the accuracy of the minimum smoothed entropy estimate, +.>。
4. The security analysis method according to claim 1, further comprising,
the receiving end publishes sequence information of part of Z-based pulses through a classical channel, and the second quantum state of the single photon in the part of Z-based pulses; the Z-based pulse is the single photon pulse measured by the receiving end by using the Z-based pulse;
and the transmitting end extracts the first quantum state of the single photon according to the partial Z-based pulse and calculates the key length by adopting a statistical average method.
5. The security analysis method of claim 4, further comprising obtaining the count and the bit error rate using a decoy state method.
6. A security analysis system based on four-state quantum communication, which performs security analysis of a quantum channel using the security analysis method according to any one of claims 1 to 5, characterized in that the security analysis system comprises,
the transmitting end comprises a light source and a coding module; the light source is a single photon source and is used for generating single photon pulses, and the coding module is used for randomly selecting and coding four quantum states on single photons of the single photon pulses to prepare first quantum states of the single photons; the four quantum states are Z0 state, Z1 state, X0 state and Y0 state respectively; the Z0 state and the Z1 state are quantum states prepared under a Z base, the X0 state is a quantum state prepared under an X base, and the Y0 state is a quantum state prepared under a Y base;
the receiving end comprises a decoding module and a single photon detector; the decoding module is used for decoding the single photon by selecting a Z base or an X base, outputting the single photon to the single photon detector and obtaining a second quantum state of the single photon;
the quantum channel is arranged between the sending end and the receiving end and is used for transmitting the single photon pulse;
classical channel, set up between stated sender and stated receiving end, used for transmitting the public information.
7. The security analysis system of claim 6, wherein the encoding module comprises a first beam splitter, a first interference ring, and a first beam combiner, the first interference ring comprising a first arm and a second arm, the first arm having a length greater than a length of the second arm;
the first beam splitter is used for splitting the single photon pulse so as to transmit the single photon pulse to the first beam combiner through the first arm and the second arm respectively; the first arm is provided with a first optical attenuator, and the second arm is provided with a second optical attenuator; when the first optical attenuator or the second optical attenuator is in a closed state, the first beam combiner outputs the quantum state under the Z base to the quantum channel.
8. The security analysis system of claim 7, wherein the encoding module further comprises a first phase modulator disposed on the first arm for generating different phase differences for single photon pulses passing through the first arm and single photon pulses passing through the second arm; when the first optical attenuator and the second optical attenuator are in the closed state, the different phase differences enable the first beam combiner to output the quantum state under the X base and the quantum state under the Y base respectively.
9. The security analysis system of claim 6, wherein the decoding module comprises a second beam splitter, a second interference ring, and a second beam combiner, the second interference ring comprising a third arm and a fourth arm, the third arm having a length greater than a length of the fourth arm;
the second beam splitter is used for transmitting the single photon pulse output by the quantum channel to the second beam combiner through the third arm and the fourth arm respectively; the third arm is provided with a third optical attenuator and a second phase modulator, and the fourth arm is provided with a fourth optical attenuator; the second beam combiner is connected with two single photon detectors;
when the third optical attenuator or the fourth optical attenuator is in a closed state, the quantum states detected by the two single photon detectors are quantum states under the Z base;
when the third optical attenuator and the fourth optical attenuator are in the closed state, the quantum states detected by the two single photon detectors are the quantum states under the X base.
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