Quantum confidential query system and method based on phase coding

Abstract

The invention relates to a quantum confidential query system and method based on phase coding, and belongs to the field of quantum communication and quantum cryptography. The system comprises a first key distribution subsystem, a second key generation subsystem and a confidential query subsystem. The method comprises the following steps: 1) a user Alice and a database holder Bob generate a first key sequence by using a first key distribution subsystem, and send the first key sequence to a second key generation subsystem; (2) Alice and Bob dilute the first key sequence into a second key sequence through a second key generation subsystem, and carry out key storage; and 3) the Alice and the Bob call the second secret key sequence through the confidential query subsystem, shift the second secret key sequence, and respectively perform encryption and decryption operations to complete confidential information retrieval. In the quantum confidential query process, the problem of limitation of a polarization coding mode is solved through a phase coding mode, so that the practical process of a quantum confidential query protocol is promoted.

Description

Technical Field

[0001] The invention belongs to the field of quantum communication and quantum cryptography, and relates to a quantum security query system and method based on phase coding. Background Art

[0002] In the Symmetrical Private Information Retrieval (SPIR) problem in the field of classical cryptography, user Alice wants to query the information of a certain entry in the database of Bob, which contains extremely valuable and sensitive content. On the one hand, from the perspective of user security, Alice does not want Bob to know the specific content of the entry she wants to query; on the other hand, from the perspective of database security, Bob does not want to reveal to Alice information other than the entry she wants to query. Traditional solutions are based on mathematically difficult problems such as factorization of large integers and solving discrete logarithms to achieve privacy security, and their security is guaranteed by computational assumptions. However, this is very fragile in front of quantum computers with powerful computing power. Fortunately, Quantum Private Query (QPQ), as a quantum solution to the SPIR problem, is considered to be another practical new quantum cryptographic protocol in addition to Quantum Key Distribution (QKD), which allows users to retrieve information from the database without revealing the query content, while also ensuring that other entry information in the database is not leaked. At present, QPQ protocols can be divided into two categories, one is the Oracle-based QPQ protocol, and the other is the QKD-based QPQ protocol. Compared with the former, the QKD-based QPQ protocol can effectively tolerate channel loss, can be extended to large databases with the help of mature QKD technology, and can be directly implemented on current quantum systems. Its protocol process is simple, with higher practical value and broader application prospects.

[0003] Most of the existing QPQ protocols are based on the polarization characteristics of photons to achieve information encoding, that is, polarization encoding is used for encoding. However, on the one hand, from the perspective of the architecture, in actual quantum communication systems, most of them use optical fibers with fluctuations, medium inhomogeneity, birefringence fluctuations, etc., which will cause the polarization state of photons to change continuously during transmission, so that the polarization state transmitted by the transmitter is inconsistent with the polarization state actually received by the receiver. In addition, factors such as the bending of the optical fiber and the change of ambient temperature can also easily cause the change of the polarization state of photons during transmission, destroying the original encoded information of the photons, thereby increasing the bit error rate of the entire communication system. On the other hand, from the perspective of encoding methods, all existing protocol participants need to prepare quantum states to transmit information, but due to the complex structure of quantum devices and the relatively high manufacturing and maintenance costs at the current technical level, if each protocol participant is required to be equipped with a large number of quantum devices, it will increase the difficulty of implementing the protocol, which is not conducive to the promotion and practical application of the protocol. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a quantum security query system and method based on phase encoding.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A quantum security query system based on phase encoding, the system comprises a first key distribution subsystem, a second key generation subsystem and a security query subsystem, the first key distribution subsystem generates a first key sequence and transmits the first key sequence to the second key generation subsystem, the second key generation subsystem generates a second key sequence according to the first key sequence and transmits the second key sequence to the security query subsystem, and the security query subsystem is used for security query;

[0007] The first key distribution subsystem includes a sending end and a receiving end, wherein the user generates a first key sequence by exchanging photon sequence information through the sending end and the database holder generates a first key sequence through the receiving end;

[0008] The second key generation subsystem includes a key storage module, a key equalization module and a key dilution module, which obtains a second key sequence by equalizing and performing bit-by-bit XOR operations on the first key sequence;

[0009] The confidentiality query subsystem includes a key shift module, an encryption module and a decryption module, wherein the database holder encrypts the database entries through the encryption module, and the user decrypts the query entries through the decryption module.

[0010] Further, the transmitting end of the first key distribution subsystem includes a light source device Laser, an adjustable optical attenuator ATT, a circulator Cir, a single photon detector SPD and a wavelength filter WF1 connected in sequence, wherein one port of the circulator Cir is connected to the adjustable optical attenuator ATT, the second port is connected to the single photon detector SPD, and the third port is connected to the wavelength filter WF1;

[0011] The receiving end of the first key distribution subsystem includes a wavelength filter WF2 and a phase encoding unit, wherein the phase encoding unit includes a polarization beam splitter PBS, an unequal-arm interferometer, a phase modulator PM and a Faraday mirror FM; the unequal-arm interferometer includes an upper arm and a lower arm, and the lower arm has a delay line DL; a first port of the polarization beam splitter PBS is connected to the wavelength filter WF2, a second port is connected to the upper arm of the unequal-arm interferometer, and a third port is connected to the lower arm of the unequal-arm interferometer; the phase modulator PM and the Faraday mirror FM form a Sagnac loop;

[0012] The sending end and the receiving end are connected through a fiber optic channel.

[0013] Furthermore, the phase modulator modulates the phase Any one of them, and only phase modulates the polarized light reflected by the Faraday mirror first; the phase modulator does not load the phase for the parallel polarized light |0>, and randomly loads the phase for the vertical polarized light |1>, which is expressed as:

[0014]

[0015] The Faraday mirror eliminates the influence of the fiber birefringence on the polarization state, and the reflected pulse returns in an orthogonal polarization mode, which is expressed as:

[0016]

[0017] The two components of the light pulse passing through the polarization beam splitter pass through the phase modulator in clockwise and counterclockwise directions respectively.

[0018] Furthermore, the working principle of the phase encoding unit is as follows: the user prepares a sequence of |ψ in > photons in the state:

[0019] |ψ in >=α|0>+β|1>

[0020] where α and β are complex numbers, |α| 2 represents the measurement quantum bit |ψ in >The probability of getting |0>, |β| 2 represents the measurement quantum bit |ψ in >The probability of getting |1> and satisfying the normalization condition |α| 2+|β| 2 =1;

[0021] Photon<ψ in > will pass through the adjustable optical attenuator ATT, circulator Cir and wavelength filter WF1 in sequence, and the adjustable optical attenuator ATT will convert the photon <ψ in >Attenuated to the single photon level, the wavelength filter WF1 filters out the invisible light signal inserted by the eavesdropper according to the wavelength, ensuring that the photon state sent by the user is a single photon state; <ψ in >The photons reach the receiving end of the database holder through the fiber optic channel;

[0022] |ψ in >state passes through the wavelength filter WF2, which filters out the invisible light signal inserted by the eavesdropper according to the wavelength to ensure that the state received by the receiving end is a single-photon state; the polarization beam splitter PBS converts the photon |ψ in > is divided into two pulses, |0> state and |1> state; in the polarization beam splitter PBS, the |0> state is transmitted from the polarization beam splitter PBS and passes through the upper arm of the unequal-arm interferometer. The specific process is as follows: the |0> state first reaches the Faraday mirror FM, the polarization angle rotates 90 degrees to the |1> state, and then passes through the polarization controller PM to load the phase It propagates in the clockwise direction to the opposite arm, i.e., the lower arm of the interferometer, and then reflects from the polarization beam splitter PBS;

[0023] The |1> state is reflected from the polarization beam splitter PBS and passes through the lower arm of the unequal-arm interferometer. The specific process is as follows: based on the setting of the delay line DL, the |1> state reaches the Faraday mirror FM, the polarization angle rotates 90 degrees and turns into the |0> state, propagates counterclockwise to the arm opposite to the previous one, that is, the upper arm of the interferometer, and is transmitted from the polarization beam splitter PBS;

[0024] The two pulses pass through the same path in opposite order and arrive at the port of the unequal-arm interferometer at the same time to interfere with each other, and the output quantum state is:

[0025]

[0026] in, and are the phases introduced by the phase encoding unit to the clockwise and counterclockwise polarization components in the entire path, ignoring and The difference between , the resulting quantum state is:

[0027]

[0028] Among them, the global phase factor brought by the entire path of the phase encoding unit to the polarization component is ignored. The final output quantum state is:

[0029]

[0030] The photons are transmitted back to the sending end via the optical fiber channel. The user uses a single photon detector SPD to detect the received quantum state and establishes the first key sequence with the database holder based on the selection of the measurement basis, the measurement results and the declaration results returned by the database holder.

[0031] Further, the key storage module of the second key generation subsystem stores the first key sequence generated by the first key distribution subsystem and the second key sequence generated by the key dilution module;

[0032] The key equalization module equally divides the received first key sequence into k sub-parts of length N, where N is the length of the database entry and k is a security parameter related to N;

[0033] The key dilution module performs a bit-by-bit XOR operation on the equally divided key sub-parts to generate a second key sequence.

[0034] Furthermore, the key shifting module of the confidentiality query subsystem shifts the second key sequence according to the user's statement to make it correspond to the entry queried by the user; the encryption module encrypts the database information according to the shifted second key sequence; and the decryption module decrypts the database information according to the shifted second key sequence.

[0035] On the other hand, the present invention also provides a quantum security query method based on the aforementioned phase-encoded quantum security query system, the method comprising the following steps:

[0036] S1: User Alice and database holder Bob use the first key distribution subsystem to generate a first key sequence and send it to the second key generation subsystem;

[0037] S2: Alice and Bob dilute the first key sequence into a second key sequence through the second key generation subsystem and store the key;

[0038] S3: Alice and Bob call the second key sequence through the confidentiality query subsystem, shift it and perform encryption and decryption operations respectively to complete the confidential information retrieval.

[0039] Further, step S1 includes the following sub-steps:

[0040] S11: Alice prepares a sequence of single photons through the light source device at the sending end of the first key distribution subsystem, and sends it to the receiving end of the database holder Bob through the optical fiber channel;

[0041] S12: Bob adjusts the phase of the n received photons through the phase encoding unit at the receiving end of the first key distribution subsystem. For any one of them, 0 and π are encoded as the classical bit 0, and π / 2 and 3π / 2 are encoded as the classical bit 1; Bob returns the adjusted photon to Alice through the optical fiber channel;

[0042] S13: Alice uses the single-photon detector at the sending end in the first key distribution subsystem to measure each photon returned by Bob, declares the position of the detected photon, and discards the undetected photons;

[0043] S14: Bob declares two quantum states for each position where Alice obtains a measurement result. One is the quantum state just sent to Alice, and the other is a random state under another set of bases, which can be expressed as:

[0044] A φ，ψ ={|φ>,|ψ>}

[0045] Among them, φ∈{+,-}, ψ∈{R,L}, and one of the states |φ> and |ψ> is returned by Bob to Alice;

[0046] S15: Alice establishes a first key sequence with Bob based on the selection of the measurement base, the measurement results, and Bob's declaration results. The sequence satisfies the following conditions:

[0047] The database holder knows all the key bits, the user only knows a part of them, and the database holder does not know which bits the user knows.

[0048] Further, in step S2, the second key generation step is: Alice and Bob use the key equalization module and the key dilution module in the second key generation subsystem to generate the first key sequence Perform equalization and dilution operations to obtain the second key sequence It is expressed as:

[0049]

[0050] This sequence satisfies the following conditions:

[0051] The database holder knows all the key bits, the user knows at least one of them, and the database holder does not know the position of the bit known by the user. If the user does not know any bit in the key, steps S1 to S2 need to be repeated.

[0052] Further, in step S3, the confidential information retrieval step is as follows: suppose Alice knows the j-th bit in the second key sequence, and she expects to query the i-th entry in the database; then Alice declares the shift value s=ji, and according to this declaration, Bob shifts the key by s bits through the shift module in the confidential query system, and then uses the shifted second key sequence to encrypt the database entry through the encryption module, and Alice decrypts it through the decryption module to obtain the entry she expects to query.

[0053] The beneficial effects of the present invention are:

[0054] The present invention encodes database information in the phase operation performed on the particles, rather than the polarization state used in the traditional polarization encoding method. This transformation is based on the significant stability advantage of phase encoding compared to polarization encoding. In polarization coding, the transmission of information depends on the polarization state of photons, but the polarization state is easily affected by external environment such as temperature, pressure and changes in the characteristics of the optical fiber itself, which leads to an increase in the bit error rate. Phase coding carries data by precisely controlling the phase information of particles, effectively reducing coding errors caused by interference from external factors, greatly reducing the bit error rate, and solving the limitations of polarization coding.

[0055] In addition, the phase encoding method can significantly reduce the requirements of the participants for quantum devices. In the present invention, only one participant needs to prepare a quantum state, and the other participant can encode it by performing certain specific phase adjustment operations, which reduces the preparation cost of quantum resources and avoids the tediousness and waste of information transmission.

[0056] In addition, the current development trend of quantum communication networks shows that phase-coded networks have shown superior performance in optical fiber communications. The present invention closely follows this technological frontier and adopts phase coding to make the proposed quantum security query method more compatible with the existing optical fiber communication quantum network. This compatibility not only improves the efficiency and reliability of information transmission, but also provides strong technical support for the practical application of quantum security query protocols.

[0057] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0059] Figure 1 Schematic diagram of quantum security query system based on phase encoding;

[0060] Figure 2 Schematic diagram of quantum confidentiality query method based on phase encoding;

[0061] Figure 3 This is a schematic diagram of the specific process of the quantum confidentiality query method based on phase encoding;

[0062] Figure 4 A schematic diagram of guessing the first key sequence for user Alice;

[0063] Figure 5 generating a schematic diagram for a second key sequence;

[0064] Figure 6 Generate a schematic diagram for the shifted second key. DETAILED DESCRIPTION

[0065] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0066] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0067] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0068] See also Figure 1 to Figure 6, which is a quantum security query system and method based on phase encoding.

[0069] like Figure 1 As shown, a quantum security query system based on phase encoding includes a first key distribution subsystem, a second key generation subsystem and a security query subsystem.

[0070] The first key distribution subsystem includes a sending end and a receiving end. Figure 1 As shown, the transmitting end includes a light source device Laser, an adjustable optical attenuator ATT, a circulator Cir, a single photon detector SPD and a wavelength filter WF1 connected in sequence. One port of the circulator Cir is connected to the adjustable optical attenuator ATT, the second port is connected to the single photon detector SPD, and the third port is connected to the wavelength filter WF1. The receiving end includes a wavelength filter WF2, a polarization beam splitter PBS, an unequal arm interferometer, a phase modulator PM and a Faraday mirror FM connected in sequence. One port of the polarization beam splitter PBS is connected to the wavelength filter WF2, the second port is connected to the upper arm (short arm) of the unequal arm interferometer, and the third port is connected to the lower arm (long arm) of the unequal arm interferometer. The unequal arm interferometer consists of an arm (short arm) and a lower arm (long arm), and the long arm has a delay line DL. The phase modulator PM and the Faraday mirror FM form a Sagnac ring. The polarization beam splitter PBS, the unequal arm interferometer and the Sagnac ring form a phase encoding unit. The transmitting end and the receiving end are connected through an optical fiber channel.

[0071] Phase modulator modulates the phase Any one of them, and only phase modulates the polarized light reflected by the Faraday mirror first. In addition, the phase modulator does not load the phase for the parallel polarized light |0>, and randomly loads the phase for the vertical polarized light |1>, which can be expressed as:

[0072]

[0073] The Faraday mirror eliminates the influence of the fiber birefringence on the polarization state, and the reflected pulse returns in an orthogonal polarization mode, which can be expressed as:

[0074]

[0075] The two components of the light pulse passing through the polarization beam splitter pass through the phase modulator in clockwise and counterclockwise directions respectively.

[0076] The phase encoding unit automatically compensates for phase drift and polarization drift, which can make up for the birefringence effect and polarization-related loss of the optical fiber, thereby reducing the bit error rate of the entire communication system.

[0077] The working principle of the phase encoding unit is as follows: User Alice prepares a sequence of phases in the range of |ψ in> photons in the state:

[0078] |ψ in >=α|0>+β|1>

[0079] where α and β are complex numbers, |α| 2 represents the measurement quantum bit |ψ in >The probability of getting |0>, |β| 2 represents the measurement quantum bit |ψ in >The probability of getting |1> and satisfying the normalization condition |α| 2 +|β| 2 =1.

[0080] This string of photons will pass through the adjustable optical attenuator ATT, the circulator Cir and the wavelength filter WF1 in sequence. The adjustable optical attenuator ATT will attenuate the photons to the single photon level. The wavelength filter WF1 can filter out the invisible light signal inserted by the eavesdropper according to the wavelength to ensure that the state sent by Alice is a single photon state. Subsequently, this string of photons passes through the optical fiber channel and reaches the receiving end of the database holder Bob.

[0081] |ψ in > state passes through the wavelength filter WF2, which can filter out the invisible light signal inserted by the eavesdropper according to the wavelength, ensuring that the state received by Bob is a single photon state. Subsequently, it is divided into two pulses, |0> state and |1> state, through the polarization beam splitter PBS. According to the working principle of the polarization beam splitter PBS, the |0> state is transmitted from the polarization beam splitter PBS and passes through the upper arm of the unequal-arm interferometer. The |1> state is reflected from the polarization beam splitter PBS and passes through the lower arm of the unequal-arm interferometer. Due to the existence of the delay line DL, the |0> state first reaches the Faraday mirror, and the polarization angle is rotated 90 degrees to transform into the |1> state, and after passing through the polarization controller PM, the phase It propagates in a clockwise direction to the opposite arm, i.e., the lower arm of the interferometer, and is reflected from the polarization beam splitter PBS. After reaching the |1> state, it reaches the Faraday mirror, and the polarization angle rotates 90 degrees to the |0> state, propagates in a counterclockwise direction to the opposite arm, i.e., the upper arm of the interferometer, and is transmitted from the polarization beam splitter PBS. The two pulses pass through the same path in opposite order, so they arrive at the port of the unequal arm interferometer at the same time to interfere, and the output quantum state is obtained as follows:

[0082]

[0083] in, and They are the phases introduced by the phase encoding unit to the polarization components propagating clockwise and counterclockwise in the entire path. Both pulses propagate clockwise and counterclockwise in a very short time. and The difference between is very small and is considered negligible. Therefore, the resulting quantum state is:

[0084]

[0085] Among them, the global phase factor brought by the entire path of the phase encoding unit to the polarization component is ignored. Because it has nothing to do with the observable properties of the quantum system, the final output quantum state is:

[0086]

[0087] The photon is transmitted back to the sender via the optical fiber channel, and Alice uses a single photon detector SPD to detect the received quantum state.

[0088] In the transmitting end and the receiving end, except for the polarization-maintaining fiber used in the phase encoding unit, the rest are single-mode fibers.

[0089] The second key generation subsystem includes a key storage module, a key distribution module and a key dilution module. The key storage module stores the first key sequence generated by the first key distribution subsystem and the second key sequence generated by the key dilution module, and waits for the call of the quantum security query subsystem. The key distribution module divides the received first key sequence into k sub-parts of length N, where N is the length of the database entry and k is a security parameter related to N. The key dilution module performs a bit-by-bit XOR operation on the sub-parts after being divided to generate a second key sequence.

[0090] The confidentiality query subsystem includes a key shift module, an encryption module and a decryption module. The key shift module shifts the second key sequence according to Alice's statement so that it corresponds to the entry queried by Alice. The encryption module encrypts the database information according to the shifted second key sequence. The decryption module decrypts the database information according to the shifted second key sequence.

[0091] A quantum confidentiality query method based on phase encoding, such as Figure 2 , Figure 3 As shown, the steps are as follows:

[0092] S1: User Alice and database holder Bob use the first key distribution subsystem to generate a first key sequence and send it to the second key generation subsystem. The steps for generating the first key sequence are:

[0093] S11: Alice prepares a sequence of single photons through the light source device at the sending end in the first key distribution subsystem, and sends it to the receiving end of the database holder Bob through the optical fiber channel.

[0094] The photons prepared by Alice can be in the |+> state:

[0095]

[0096] Then the sequence of single photons is:

[0097] {|+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>, |+>}

[0098] S12: Bob adjusts the phase of the n received photons through the phase encoding unit at the receiving end of the first key distribution subsystem. Any one of them, 0 and π are encoded as the classical bit 0, and π / 2 and 3π / 2 are encoded as the classical bit 1. He then returns the adjusted photon to Alice through the fiber optic channel.

[0099] The phase-modulated photon in the |+> state is any one of {|+>, |->, |R>, |L>}, where:

[0100]

[0101] Bob's phase modulation can be:

[0102]

[0103] Then the photon after phase adjustment is:

[0104] {|R>, |+>, |+>, |->, |L>, |->, |->, |L>, |R>, |->, |+>, |L>, |R>, |+>, |L>, |->}

[0105] Bob's first key sequence is:

[0106] {1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0}

[0107] S13: Alice uses the single-photon detector at the sending end in the first key distribution subsystem to measure each photon returned by Bob, declares the position of the detected photon, and discards the undetected photons;

[0108] The measurement basis chosen by Alice can be:

[0109] {X,X,Y,Y,X,Y,Y,X,X,Y,Y,X,X,Y,X,Y}

[0110] Alice's measurement result can be:

[0111] {|->, |+>, |L>, |R>, |+>, |R>, |L>, |->, |->, |L>, |R>, |+>, |->, |R>, |->, |L>}

[0112] S14: Bob declares two quantum states for each position where Alice obtains the result of the measurement. One is the quantum state just sent to Alice, and the other is a random quantum state under another set of bases, which can be expressed as:

[0113] A φ，ψ ={|φ>,|ψ>}

[0114] Among them, φ∈{+,-}ψ∈{R,L}, and one of the states |φ> and |ψ> is returned by Bob to Alice. Then the quantum state pair declared by Bob can be:

[0115] {|+>, |R>}, {|+>, |R>}, {|+>, |L>}, {|->, |R>}, {|+>, |L>}, {|->, |L>}, {|->, |L>}, {|->, |L>} , {|->, |R>}, {|->, |L>}, {|+>, |R>}, {|+>, |L>}, {|->, |R>}, {|+>, |L>}, {|+>, |L>}, {|->, |L>}

[0116] S15: Alice establishes a first key sequence with Bob based on the selection of the measurement base, the measurement result and Bob's declaration result. The sequence satisfies that Bob knows all the key bits, Alice only knows a part of the bits, and Bob does not know which part of the bits Alice knows.

[0117] Alice records the quantum states that can be deduced as the corresponding bits, and the quantum states that cannot be deduced as "*". Alice deduces the first key sequence diagram as follows Figure 4 As shown. For example, the quantum state sent by Bob is |+>. Assuming that he declares that the quantum state pair is {|+>, |R>}, then when Alice uses the Y basis to measure |L>, it can be deduced that what Bob sent is |+>. Because Alice will definitely get the |R> state when measuring the |R> state with the Y basis, and may get the |R> state or the |L> state when measuring the |+> state with the Y basis. The probability that Alice chooses the Y basis for measurement is 1 / 2, and there is also a 1 / 2 probability of obtaining the measurement result |L>. It can be obtained that Alice has a 1 / 4 probability of obtaining a deterministic result and a 3 / 4 probability of obtaining an uncertain result. According to her choice of measurement basis, the measurement result and Bob's declaration, Alice's first key sequence is:

[0118] {1, *, *, 0, *, *, *, *, *, 0, 1, *}

[0119] S2: Alice and Bob convert the first key sequence into the second key sequence through the second key generation subsystem and store the key. The steps for generating the second key sequence are:

[0120] Alice and Bob use the key sharing module and key dilution module in the second key generation subsystem to generate the first key sequence Perform equalization and dilution operations to obtain the second key sequence It can be described as:

[0121]

[0122] like Figure 5 As shown, the key equalization module divides the received first key sequence into k sub-parts of length N, where the length of the database entry N = 8, and the security parameter k related to N = 2. After being equally divided, Bob's first key sequence can be expressed as:

[0123] {1, 0, 0, 0, 1, 0, 0, 1}

[0124] {1, 0, 0, 1, 1, 0, 1, 0}

[0125] Alice's first key sequence can be expressed as follows after being equally divided:

[0126] {1, *, *, 0, *}

[0127] {, *, *, *, 0, 1, *}

[0128] The key dilution module performs a bit-by-bit XOR operation on the two equally divided sub-parts to generate a second key sequence. Bob's second key sequence can be expressed as:

[0129] {0, 0, 0, 1, 0, 0, 1, 1}

[0130] Alice's second key sequence can be expressed as:

[0131] {, *, *, *, 0, *, *}

[0132] The second key sequence satisfies that Bob knows all the key bits, Alice knows at least one of them, Bob does not know the position of the bits known by Alice, and stores them in the key storage module.

[0133] S3: Alice and Bob call the second key sequence through the confidentiality query subsystem, shift it and perform encryption and decryption operations to complete the confidential information retrieval. The confidential information retrieval steps are:

[0134] If Alice knows the jth bit in the second key sequence, but the information she wants to obtain is located in the entry in the database, then Alice declares the shift value s=ji. According to this declaration, Bob shifts the key by s bits through the shift module in the confidentiality query system, and then uses the shifted second key sequence to encrypt the database entry through the encryption module. Alice decrypts it through the decryption module to obtain the entry she wants to query. Figure 6 As shown in the figure, Alice knows the 6th bit in the second key sequence, but the information she wants to obtain is located in the 4th entry of the database. At this time, Alice declares the shift value s=ji=2, and when s<0, the key is shifted right, and when s>0, the key is shifted left. According to this declaration, Bob shifts the key left by 2 bits through the shift module. The second key sequence after Bob's shift can be expressed as:

[0135] {0, 1, 0, 0, 1, 1, 0, 0}

[0136] Bob then uses this key sequence to encrypt the database entry through the encryption module.

[0137] Alice's second key sequence after shifting can be expressed as:

[0138] {, *, *, 0, *, *, *}

[0139] Alice then uses this key to decrypt through the decryption module to obtain the entry she wants to query.

[0140] The present invention encodes the database information on the phase operation performed on the particles, rather than on the polarization state in the polarization encoding method. The phase encoding method is more stable, can reduce the bit error rate caused by the change of polarization state, and solve the limitation problem of polarization encoding. In addition, the present invention uses phase encoding to significantly reduce the requirements of participants on quantum devices and the preparation cost of quantum resources, and also avoids the cumbersomeness and waste of information transmission. In addition, most of the existing quantum communication networks are phase-coded networks with good performance in optical fiber communications. The present invention can be better applied to the current optical fiber communication quantum network, thereby promoting the practical application of quantum security query protocols.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A quantum security query system based on phase encoding, characterized in that: The system comprises a first key distribution subsystem, a second key generation subsystem and a confidentiality query subsystem, wherein the first key distribution subsystem generates a first key sequence and transmits the first key sequence to the second key generation subsystem, the second key generation subsystem generates a second key sequence according to the first key sequence and transmits the second key sequence to the confidentiality query subsystem, and the confidentiality query subsystem is used for confidentiality query; The first key distribution subsystem includes a transmitting end and a receiving end, wherein the user generates a first key sequence by performing photon sequence information interaction through the transmitting end and the database holder generates a first key sequence through the receiving end; The second key generation subsystem includes a key storage module, a key equalization module and a key dilution module, which obtains a second key sequence by equalizing and performing bit-by-bit XOR operations on the first key sequence; The confidentiality query subsystem includes a key shift module, an encryption module and a decryption module, wherein the database holder encrypts the database entries through the encryption module, and the user decrypts the query entries through the decryption module.

2. According to claim 1, a phase-encoded quantum security query system is characterized by: The transmitting end of the first key distribution subsystem includes a light source device Laser, an adjustable optical attenuator ATT, a circulator Cir, a single photon detector SPD and a wavelength filter WF1 connected in sequence, wherein one port of the circulator Cir is connected to the adjustable optical attenuator ATT, the second port is connected to the single photon detector SPD, and the third port is connected to the wavelength filter WF1; The receiving end of the first key distribution subsystem includes a wavelength filter WF2 and a phase encoding unit, wherein the phase encoding unit includes a polarization beam splitter PBS, an unequal-arm interferometer, a phase modulator PM and a Faraday mirror FM; the unequal-arm interferometer includes an upper arm and a lower arm, and the lower arm has a delay line DL; a first port of the polarization beam splitter PBS is connected to the wavelength filter WF2, a second port is connected to the upper arm of the unequal-arm interferometer, and a third port is connected to the lower arm of the unequal-arm interferometer; the phase modulator PM and the Faraday mirror FM form a Sagnac ring; The sending end and the receiving end are connected through a fiber optic channel.

3. A phase-encoded quantum security query system according to claim 2, characterized in that: Phase modulator modulates the phase Any one of them, and only phase modulates the polarized light reflected by the Faraday mirror first; the phase modulator does not load the phase for the parallel polarized light |0>, and randomly loads the phase for the vertical polarized light |1>, which is expressed as: The Faraday mirror eliminates the influence of the fiber birefringence on the polarization state, and the reflected pulse returns in an orthogonal polarization mode, which is expressed as: The two components of the light pulse passing through the polarization beam splitter pass through the phase modulator in clockwise and counterclockwise directions respectively.

4. A phase-encoded quantum security query system according to claim 3, characterized in that: The working principle of the phase encoding unit is as follows: the user prepares a sequence of phases in the range of |ψ in > photons in the state: |ψ in >=a|0>+b|1> where α and β are complex numbers, |α| 2 represents the measurement quantum bit |ψ in >The probability of getting |0>, |β| 2 represents the measurement quantum bit |ψ in >The probability of getting |1> and satisfying the normalization condition |α| 2 +|β| 2 =1; Photon|ψ in > will pass through the adjustable optical attenuator ATT, circulator Cir and wavelength filter WF1 in sequence. The adjustable optical attenuator ATT will convert the photon |ψ in >Attenuated to the single photon level, the wavelength filter WF1 filters out the invisible light signal inserted by the eavesdropper according to the wavelength, ensuring that the photon state sent by the user is a single photon state; |ψ in >The photons reach the receiving end of the database holder through the fiber optic channel; |ψ in >state passes through the wavelength filter WF2, which filters out the invisible light signal inserted by the eavesdropper according to the wavelength to ensure that the state received by the receiving end is a single-photon state; the polarization beam splitter PBS converts the photon |ψ in > is divided into two pulses, |0> state and |1> state; in the polarization beam splitter PBS, the |0> state is transmitted from the polarization beam splitter PBS and passes through the upper arm of the unequal-arm interferometer. The specific process is as follows: the |0> state first reaches the Faraday mirror FM, the polarization angle rotates 90 degrees to the |1> state, and then passes through the polarization controller PM to load the phase It propagates in the clockwise direction to the opposite arm, i.e., the lower arm of the interferometer, and then reflects from the polarization beam splitter PBS; The |1> state is reflected from the polarization beam splitter PBS and passes through the lower arm of the unequal-arm interferometer. The specific process is as follows: based on the setting of the delay line DL, the |1> state reaches the Faraday mirror FM, the polarization angle rotates 90 degrees and turns into the |0> state, propagates counterclockwise to the arm opposite to the previous one, that is, the upper arm of the interferometer, and is transmitted from the polarization beam splitter PBS; The two pulses pass through the same path in opposite order and arrive at the port of the unequal-arm interferometer at the same time to interfere with each other, and the output quantum state is: in, and are the phases introduced by the phase encoding unit to the clockwise and counterclockwise polarization components in the entire path, ignoring and The difference between , the resulting quantum state is: Among them, the global phase factor brought by the entire path of the phase encoding unit to the polarization component is ignored. The final output quantum state is: The photons are transmitted back to the sending end via the optical fiber channel. The user uses a single photon detector SPD to detect the received quantum state and establishes the first key sequence with the database holder based on the selection of the measurement basis, the measurement results and the declaration results returned by the database holder.

5. A phase-encoded quantum security query system according to claim 4, characterized in that: The key storage module of the second key generation subsystem stores the first key sequence generated by the first key distribution subsystem and the second key sequence generated by the key dilution module; The key equalization module equally divides the received first key sequence into k sub-parts of length N, where N is the length of the database entry and k is a security parameter related to N; The key dilution module performs a bit-by-bit XOR operation on the equally divided key sub-parts to generate a second key sequence.

6. A phase-encoded quantum security query system according to claim 5, characterized in that: The key shift module of the confidentiality query subsystem shifts the second key sequence according to the user's statement to make it correspond to the entry queried by the user; the encryption module encrypts the database information according to the shifted second key sequence; and the decryption module decrypts the database information according to the shifted second key sequence.

7. A quantum security query method based on the phase-coded quantum security query system according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: S1: User Alice and database holder Bob use the first key distribution subsystem to generate a first key sequence and send it to the second key generation subsystem; S2: Alice and Bob dilute the first key sequence into a second key sequence through the second key generation subsystem and store the key; S3: Alice and Bob call the second key sequence through the confidentiality query subsystem, shift it and perform encryption and decryption operations respectively to complete the confidential information retrieval.

8. The phase-encoded quantum security query method according to claim 7, characterized in that: Step S1 includes the following sub-steps: S11: Alice prepares a sequence of single photons through the light source device at the sending end of the first key distribution subsystem, and sends it to the receiving end of the database holder Bob through the optical fiber channel; S12: Bob adjusts the phase of the n received photons through the phase encoding unit at the receiving end of the first key distribution subsystem. For any one of them, 0 and π are encoded as the classical bit 0, and π / 2 and 3π / 2 are encoded as the classical bit 1; Bob returns the adjusted photon to Alice through the optical fiber channel; S13: Alice uses the single-photon detector at the sending end in the first key distribution subsystem to measure each photon returned by Bob, declares the position of the detected photon, and discards the undetected photons; S14: Bob declares two quantum states for each position where Alice obtains a measurement result. One is the quantum state just sent to Alice, and the other is a random state under another set of bases, which can be expressed as: A φ,ψ ={|φ>,ψ>} Among them, φ∈{+,-},ψ∈{R,L}, and one of the states |φ> and |ψ> is returned by Bob to Alice; S15: Alice establishes a first key sequence with Bob based on the selection of the measurement base, the measurement result, and Bob's declaration result; the sequence satisfies the following conditions: The database holder knows all the key bits, the user only knows a part of them, and the database holder does not know which bits the user knows.

9. The phase-encoded quantum security query method according to claim 8, characterized in that: In step S2, the second key generation step is as follows: Alice and Bob use the key equalization module and the key dilution module in the second key generation subsystem to generate the first key sequence Perform equalization and dilution operations to obtain the second key sequence It is expressed as: This sequence satisfies the following conditions: The database holder knows all the key bits, the user knows at least one of them, and the database holder does not know the position of the bit known by the user; if the user does not know any bit in the key, steps S1 to S2 need to be repeated.

10. A quantum security query method based on phase coding according to claim 9, characterized in that: In step S3, the confidential information retrieval step is as follows: suppose Alice knows the j-th bit in the second key sequence, and she expects to query the i-th entry in the database; then Alice declares the shift value s=ji, and according to this declaration, Bob shifts the key by s bits through the shift module in the confidential query system, and then uses the shifted second key sequence to encrypt the database entry through the encryption module, and Alice decrypts it through the decryption module to obtain the entry she expects to query.

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