Phase-encoded quantum secure query system and method

Abstract

The present application relates to a kind of quantum secure query system and method based on phase encoding, belong to quantum communication and quantum cryptography field.The system includes first key distribution subsystem, second key generation subsystem and secure query subsystem.The method steps are:1) user Alice and database holder Bob utilize first key distribution subsystem to generate first key sequence, and send it to second key generation subsystem;2)Alice and Bob dilute first key sequence into second key sequence by second key generation subsystem, and carry out key storage;3)Alice and Bob call second key sequence by secure query subsystem, respectively after shifting, carry out encryption and decryption operation, complete secure information retrieval.The present application solves the limitation problem existing in polarization encoding mode in the process of quantum secure query, to promote the practical process of quantum secure query protocol.

Description

Technical Field

[0001] The present 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 classical cryptographic problem of Symmetrical Private Information Retrieval (SPIR), a user named Alice wants to retrieve information about a specific entry from Bob, the owner of a database containing extremely valuable and sensitive data. For user security, Alice does not want Bob to know the specific content of the entry she is looking for; for database security, Bob does not want to reveal information beyond the entry she is looking for. Traditional solutions rely on mathematically difficult problems such as factoring large integers and solving discrete logarithms to achieve privacy, relying on computational assumptions. However, these solutions are vulnerable to the powerful computational power of quantum computers. Fortunately, quantum private query (QPQ), a quantum solution to the SPIR problem, is considered a practical new quantum cryptographic protocol, in addition to quantum key distribution (QKD). It allows users to retrieve information from a database without revealing the query content, while also ensuring that other database entries are not leaked. Currently, QPQ protocols can be divided into two categories: Oracle-based QPQ protocols and QKD-based QPQ protocols. Compared to the Oracle-based QPQ protocols, QKD-based QPQ protocols can effectively tolerate channel losses, can be extended to large databases using mature QKD technology, and can be directly implemented on current quantum systems. Their protocol flow is simple, offering greater practical value and broader application prospects.

[0003] Most existing QPQ protocols encode information based on the polarization properties of photons, employing polarization encoding. However, from an architectural perspective, practical quantum communication systems often utilize optical fibers, which are subject to fluctuations, dielectric inhomogeneities, and birefringence fluctuations. This causes the polarization state of photons to continuously shift during transmission, resulting in inconsistencies between the polarization state transmitted by the transmitter and the polarization state actually received by the receiver. Furthermore, factors such as fiber bending and ambient temperature fluctuations can easily cause photon polarization state changes during transmission, destroying the information originally encoded in the photons and increasing the bit error rate (BER) of the entire communication system. Furthermore, from an encoding perspective, existing protocol participants need to prepare quantum states to transmit information. However, due to the complex construction of quantum devices and the relatively high manufacturing and maintenance costs at current technological levels, requiring each protocol participant to equip themselves with a large number of quantum devices would increase the complexity of protocol implementation and hinder its widespread adoption and practical application. Summary of the Invention

[0004] In view of this, the 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, comprising 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 based on the first key sequence and transmits the second key sequence to the security query subsystem. 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 interacts with the database holder through the sending end and the receiving end to generate a first key sequence through photon sequence information exchange;

[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] Furthermore, 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; the polarization beam splitter PBS has a first port connected to the wavelength filter WF2, a second port connected to the upper arm of the unequal-arm interferometer, and a third port 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 string of |ψ in >state photons:

[0019] |ψ in >=α|0>+β|1>

[0020] Here, 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 obtaining |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 >Decayed 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, ensuring 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; among them, 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 is rotated 90 degrees to transform into the |1> state, and then the phase is loaded after passing through the polarization controller PM. It propagates in a 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 delay line DL, the |1> state reaches the Faraday mirror FM, where the polarization angle is rotated 90 degrees and transformed into the |0> state. It then propagates counterclockwise to the opposite arm, 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 a 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] Furthermore, 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 splitting module splits 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 exclusive OR operation on the equally divided key sub-parts to generate a second key sequence.

[0034] Furthermore, the key shift module of the confidentiality query subsystem shifts the second key sequence according to the user's statement so that it corresponds 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 owner 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] Furthermore, step S1 includes the following sub-steps:

[0040] S11: Alice generates a sequence of single photons using the light source device at the transmitting 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 of 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 in another basis, 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. This 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] Furthermore, in step S2, the second key generation step is as follows: Alice and Bob use the key equalization module and key dilution module in the second key generation subsystem to generate the first key sequence Perform equal division and dilution operations to obtain the second key sequence Expressed as:

[0049]

[0050] The sequence satisfies the following conditions:

[0051] The database owner knows all the key bits, and the user knows at least one of them. The database owner 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] Furthermore, 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 traditional polarization encoding. This transformation is based on the significant stability advantage of phase encoding compared to polarization encoding. In polarization encoding, the transmission of information depends on the polarization state of the photon, but the polarization state is easily affected by external environmental factors 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 encoding, on the other hand, carries data by precisely controlling the phase information of the particles, effectively reducing coding errors caused by interference from external factors, greatly reducing the bit error rate, and solving the limitations of polarization encoding.

[0055] Furthermore, phase encoding significantly reduces the quantum equipment requirements of each participant. In this method, only one participant needs to prepare a quantum state, and the other participant can perform certain phase adjustment operations to encode it. This reduces the cost of preparing quantum resources and avoids the tedious and wasteful transmission of information.

[0056] Furthermore, current development trends in quantum communication networks indicate that phase-coded networks exhibit superior performance in optical fiber communications. This invention closely follows this technological frontier. By employing phase encoding, the proposed quantum security query method is more compatible with existing optical fiber communication quantum networks. 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, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may 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 with reference to the accompanying drawings, in which:

[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 Schematic diagram of the first key sequence estimated 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 means of 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 are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

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

[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 there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional 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 Figures 1 to 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, which are connected in sequence. One port of the circulator Cir is connected to the adjustable optical attenuator ATT, its second port is connected to the single-photon detector SPD, and its 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, which are connected in sequence. One port of the polarization beam splitter PBS is connected to the wavelength filter WF2, its second port is connected to the upper arm (short arm) of the unequal-arm interferometer, and its third port is connected to the lower arm (long arm) of the unequal-arm interferometer. The unequal-arm interferometer consists of an upper arm (short arm) and a lower arm (long arm), with the long arm having a delay line DL. The phase modulator PM and the Faraday mirror FM form a Sagnac loop. The polarization beam splitter PBS, the unequal-arm interferometer, and the Sagnac loop form a phase encoding unit. The transmitting and receiving ends are connected via a fiber optic channel.

[0071] Phase modulator modulated phase Any one of them, and only phase modulates the polarized light that is first reflected by the Faraday mirror. 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. 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-dependent 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 string of |ψ in>state photons:

[0078] |ψ in >=α|0>+β|1>

[0079] Here, 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 obtaining |1> and satisfying the normalization condition |α| 2 +|β| 2 =1.

[0080] This string of photons passes through the adjustable optical attenuator (ATT), the circulator (Cir), and the wavelength filter (WF1). The ATT attenuates the photons to single photon levels, while the wavelength filter (WF1) filters out invisible light signals inserted by eavesdroppers based on their wavelength, ensuring that the state Alice transmits is a single photon. This string of photons then travels through the optical fiber channel to the receiving end of Bob, the database holder.

[0081] |ψ in The |0> state passes through wavelength filter WF2, which filters out the invisible light signal inserted by the eavesdropper based on wavelength, ensuring that the state Bob receives is a single-photon state. Subsequently, the |0> state and the |1> state are split into two pulses by the polarization beam splitter PBS. According to the operating principle of the polarization beam splitter PBS, the |0> state is transmitted through 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 presence of the delay line DL, the |0> state first reaches the Faraday mirror, where its polarization angle is rotated 90 degrees to transform it into the |1> state. After passing through the polarization controller PM, the phase shift is applied. It propagates clockwise to the opposite arm, 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, where its polarization angle rotates 90 degrees and transforms to the |0> state. It then propagates counterclockwise to the opposite arm, the upper arm of the interferometer, and is transmitted from the polarization beam splitter (PBS). The two pulses travel the same path in opposite order, and therefore arrive at the ports of the unequal-arm interferometer simultaneously, where they interfere and the resulting output quantum state is:

[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 respectively in a very short time. and The difference between them is very small and can be considered negligible. Therefore, the quantum state obtained 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 is independent of 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] At 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 averaging 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, awaiting invocation by the quantum security query subsystem. The key averaging 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 exclusive-OR operation on the divided sub-parts to generate the 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 based on Alice's declaration to correspond to the entry Alice is querying. The encryption module encrypts the database information using the shifted second key sequence. The decryption module decrypts the database information using 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 owner 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. For any of the two, 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 optical fiber 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 of 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] Alice's chosen measurement basis 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 a measurement result. One is the quantum state just sent to Alice, and the other is a random quantum state in another basis, 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 measurement base she selected, the measurement results, and Bob's declaration. This sequence ensures that Bob knows all the key bits, while Alice only knows a portion of them. Bob is unaware 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 Alice can only deduce that what Bob sent is |+> when she measures |L> using the Y basis. Because Alice will definitely get the |R> state when measuring the |R> state using the Y basis, and may get the |R> state or the |L> state when measuring the |+> state using 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 getting 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 use the second key generation subsystem to convert the first key sequence into a second key sequence and store the key. The steps for generating the second key sequence are:

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

[0121]

[0122] like Figure 5 As shown, the key splitting module splits 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 split, 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 divided equally:

[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 key bits, Alice knows at least one of them, Bob does not know the position of the bit known by Alice, and stores it 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 jth entry in the database, then Alice declares the shift value s=ji. Based on this declaration, Bob shifts the key by s bits using the shift module in the security query system. Then, he uses the shifted second key sequence to encrypt the database entry through the encryption module. Alice then decrypts the database entry using the decryption module to obtain the entry she wants to query. Figure 6 As shown, Alice knows the sixth bit of the second key sequence, but the information she wants to obtain is located in the fourth entry in the database. At this point, Alice declares a shift value s = ji = 2, and when s < 0, the key is shifted right, and when s > 0, the key is shifted left. Based on this declaration, Bob uses the shift module to shift the key left by 2 bits. 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 the entry through the decryption module to obtain the entry she wants to query.

[0140] The present invention encodes database information in the phase operation performed on the particles, rather than in the polarization state in the polarization encoding method. The phase encoding method is more stable, which 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 the phase encoding method to significantly reduce the requirements of participants for quantum equipment and the preparation cost of quantum resources, and also avoids the tediousness and waste of information transmission. In addition, the vast majority of existing quantum communication networks are phase-coded networks with good performance in optical fiber communication. The present invention can be better applied to the current optical fiber communication quantum network, thereby promoting the practical application of quantum confidentiality query protocol.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. 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 solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A quantum security query system based on phase encoding, characterized by: The system includes a first key distribution subsystem, a second key generation subsystem, and a confidentiality 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 based on the first key sequence and transmits the second key sequence to the confidentiality query subsystem. The confidentiality query subsystem is used for confidentiality query. The first key distribution subsystem includes a sending end and a receiving end, wherein the user interacts with the photon sequence information through the sending end and the database holder interacts with the database holder through the receiving end to generate a first key sequence; 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; 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 loop; The sending and receiving ends are connected via a fiber optic channel; Phase modulator modulated phase Any one of them, and only phase modulates the polarized light reflected by the Faraday mirror first; the phase modulator modulates the parallel polarized light No phase loading, for vertically polarized light Random loading phase, 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.

2. A quantum secure query system based on phase encoding according to claim 1, characterized in that: The working principle of the phase encoding unit is as follows: the user prepares a string of phases in the first key sequence distribution system through the light source device. Photons in the state: in, and It is plural. Represents the measurement qubit get The probability of Represents the measurement qubit get The probability of , and satisfy the normalization condition ; photons The photons will pass through the adjustable optical attenuator ATT, circulator Cir and wavelength filter WF1 in sequence. 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; The photons travel through the fiber optic channel to the receiving end of the database holder; The state passes through the wavelength filter WF2, which filters out the invisible light signal inserted by the eavesdropper according to the wavelength, ensuring that the state received by the receiving end is a single photon state; the polarization beam splitter PBS converts the photon Split into two pulses State and state; wherein, in the polarization beam splitter PBS, The 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 state first reaches the Faraday mirror FM, and the polarization angle rotates 90 degrees to state, and then loaded with phase after passing through the polarization controller PM , propagates in the clockwise direction to the arm opposite to the previous one, i.e. the lower arm of the interferometer, and then reflects from the polarization beam splitter PBS; The 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, After reaching the Faraday mirror FM, the polarization angle rotates 90 degrees and becomes The 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 a 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.

3. A quantum secure query system based on phase coding according to claim 2, 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 divides the received first key sequence into The length is sub-parts of is the length of the database entry, Is a relevant safety parameters; The key dilution module performs a bit-by-bit XOR operation on the equally divided key sub-parts to generate a second key sequence.

4. A phase-encoded quantum security query system according to claim 3, 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.

5. A quantum security query method based on the phase-coded quantum security query system according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: S1: User Alice and database owner 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.

6. The phase-encoded quantum security query method according to claim 5, characterized in that: Step S1 includes the following sub-steps: S11: Alice generates a sequence of single photons using the light source device at the transmitting 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 receives the received Photons are phase-adjusted, and the phase Any one of and Encoded as the classic bit 0, and Encoded as a classical bit 1; Bob returns the adjusted photon to Alice through the fiber channel; S13: Alice uses the single-photon detector at the sending end of 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 in another basis, which can be expressed as: in, ,and and There is a state in it that Bob returns to Alice; S15: Alice establishes a first key sequence with Bob based on the selection of the measurement base, the measurement results, and Bob's declaration. The first key 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.

7. The phase-encoded quantum security query method according to claim 6, characterized in that: In step S2, the second key generation step is as follows: Alice and Bob use the key equalization module and key dilution module in the second key generation subsystem to generate the first key sequence Perform equal division and dilution operations to obtain the second key sequence , expressed as: The sequence satisfies the following conditions: The database holder knows all the key bits, and the user knows at least one of them. 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.

8. The phase-encoded quantum security query method according to claim 7, characterized in that: In step S3, the confidential information retrieval step is: suppose Alice knows the first bits, the expected query is located in the database entries; then Alice declares the shift value , Bob moves the key to bits, 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 wants to query.

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