A ciphertext operation-based encrypted value range evaluation method and system

Abstract

This application provides a method and system for evaluating the value range of encrypted data based on ciphertext operations, belonging to the field of data encryption computing technology. The method involves: a user generating a homomorphic encryption key pair and a confusion circuit key pair; using the public key to encrypt sensitive data, the lower limit of the value range, and the upper limit of the value range, respectively, obtaining ciphertext of the data, the lower limit, and the upper limit, and sending the ciphertext to a service provider for storage; the user constructing a Boolean confusion circuit based on the private key in the confusion circuit key pair and the homomorphic decryption algorithm, and sending the lower limit, the upper limit, and the Boolean confusion circuit to the service provider; the service provider obtaining the ciphertext, calculating the first and second ciphertext differences with the lower limit ciphertext and the upper limit ciphertext, respectively, and extracting the corresponding sign bit ciphertext; inputting the sign bit ciphertext into the confusion circuit to obtain the confused value and returning it to the user; and the user using the public key to decrypt and obtain the evaluation result. This invention enables value range determination in the ciphertext state, protecting data privacy.

Description

Technical Field

[0001] This application belongs to the field of data encryption computing technology, specifically relating to a method and system for evaluating the range of encrypted values ​​based on ciphertext operations. Background Technology

[0002] With the widespread adoption of cloud computing and big data technologies, data holders often outsource data storage to cloud servers for cost and management convenience. To prevent data leakage, sensitive data is typically encrypted before storage. However, there is an inherent contradiction between encrypted data and efficient data utilization. In scenarios such as financial risk control and medical data sharing, users frequently need to perform value range checks on encrypted data in the cloud (e.g., determining whether a transaction amount is within a normal range) to complete compliance audits or anomaly detection. Traditional solutions usually require the cloud server to decrypt the encrypted data before performing range checks, which directly compromises data confidentiality.

[0003] In existing technologies, the comparison and range determination of ciphertext data mainly rely on secure multi-party computation or homomorphic encryption schemes. While secure multi-party computation (such as protocols based on obfuscated circuits or secret sharing) can protect input privacy, its communication complexity is typically high, especially when there are many participants or deep circuits, resulting in significant performance overhead. Homomorphic encryption schemes, such as CKKS, support floating-point arithmetic, but do not directly support ciphertext comparison operations. Existing schemes often require the construction of complex approximate comparison functions, which not only incurs high computational overhead but may also introduce unacceptable errors. Furthermore, while homomorphic encryption schemes based on TFHE and other Boolean circuits can achieve accurate comparisons, relying entirely on homomorphic logic gates to build the comparison circuit (such as a borrow chain after subtraction) results in a linear increase in the number of bootstraps with the bit width, leaving room for improvement in computational efficiency.

[0004] Therefore, there is an urgent need for a method that can both protect data privacy and efficiently and accurately assess the value range of encrypted data in the cloud. Summary of the Invention

[0005] In a first aspect, embodiments of this application provide a method for evaluating the range of encrypted values ​​based on ciphertext operations, comprising the following steps: S1. The user generates a homomorphic encryption key pair and a scrambling circuit key pair. The user uses the public key in the homomorphic encryption key pair to encrypt the sensitive data, the lower limit of the value range, and the upper limit of the value range, respectively, to obtain the data ciphertext, the lower limit ciphertext, and the upper limit ciphertext. The data ciphertext is then sent to the service provider for storage in advance. S2. The user constructs a Boolean obfuscation circuit for decrypting the symbol bits and performing logical operations based on the private key in the obfuscation circuit key pair and the homomorphic decryption algorithm, and sends the lower limit ciphertext, the upper limit ciphertext, and the Boolean obfuscation circuit to the service provider. S3. The service provider obtains the stored encrypted data, uses a homomorphic encryption algorithm to calculate the first ciphertext difference between the encrypted data and the lower bound ciphertext, and the second ciphertext difference between the upper bound ciphertext and the encrypted data, and extracts the ciphertext corresponding to the sign bit from the first ciphertext difference and the second ciphertext difference, respectively, as the first sign bit ciphertext and the second sign bit ciphertext. S4. The service provider inputs the first symbol bit ciphertext and the second symbol bit ciphertext into the Boolean obfuscation circuit to run, obtains the obfuscated value representing the evaluation result, and returns it to the user. S5. The user uses the public key in the obfuscated circuit key pair to decrypt the obfuscated value and obtain the final evaluation result of whether the sensitive data is within the value range.

[0006] Furthermore, the specific steps of step S1 are as follows: S11. The user runs the key generation function of the TFHE homomorphic encryption algorithm to generate homomorphic encryption key pairs:

[0007] in, The private key for a homomorphic encryption key pair. The public key of the homomorphic encryption key pair; S12. The user runs the key generation function of the obfuscation circuit to generate obfuscation circuit key pairs:

[0008] in, To obfuscate the private key of the circuit key pair The public key for the obfuscated circuit key pair; S13. The user side represents sensitive data, lower limit of value range, and upper limit of value range as binary bit sequences respectively; among them, integers are encoded using binary two's complement and the most significant bit is reserved as the sign bit, and floating-point numbers are encoded using the IEEE 754 single-precision standard; S14. The public key of the homomorphic encryption key pair used by the user. Perform homomorphic encryption on each bit of the binary bit sequence containing the sensitive data, the lower limit of the value range, and the upper limit of the value range to obtain the ciphertext. Lower limit ciphertext and the upper limit ciphertext ; S15. The user will encrypt the data. It is sent in advance to the service provider's storage.

[0009] Furthermore, the specific steps of step S14 are as follows: S141. The user takes sensitive data, lower limit of value range and upper limit of value range as data to be encrypted, and obtains the binary bit sequence of the data to be encrypted. The length of the binary bit sequence is L. For integer data, the binary bit sequence includes the most significant bit as the sign bit and the subsequent value bits. S142. The user extends the least significant bit of the binary bit sequence by one padding bit to obtain an extended bit sequence of length L+1; the plaintext value of the padding bit is 0. S143. The user uses the public key of the homomorphic encryption key pair. Each bit in the extended bit sequence is independently encrypted using LWE to generate the corresponding independent bit ciphertext, thus obtaining a ciphertext sequence containing L+1 bit ciphertext, where the ciphertext corresponding to the padding bit is the padding bit ciphertext. S144. The user ciphers the data corresponding to the sensitive data in the ciphertext sequence. The lower limit ciphertext corresponding to the lower limit of the value range Or the upper limit ciphertext corresponding to the upper limit of the value range Output.

[0010] Furthermore, the specific steps of step S2 are as follows: S21. The user constructs a private key based on the homomorphic decryption algorithm, which only accepts single-bit symbolic ciphertext and homomorphic encryption key pairs. Each bit is used as the input layer; S22. The user side constructs a decryption layer based on the LWE single-bit decryption gate circuit to decrypt the two-sign-bit ciphertext input to obtain two plaintext sign bits; S23. The user constructs a logic operation layer, which has a built-in OR gate for performing an OR logic operation on the two plaintext symbol bits obtained by decryption; S24. The user constructs an output layer to map the output of the OR gate to a Boolean decision label as an obfuscation value; S25. The user uses the public key of the obfuscated circuit key pair. All gate circuits in the input layer, decryption layer, logic operation layer, and output layer are encrypted and scrambled to generate the final Boolean obfuscated circuit; S26. The user will send the lower limit ciphertext. Upper limit ciphertext And Boolean confusing circuitry sent to the service provider.

[0011] Furthermore, the LWE single-bit decryption gate circuit in step S22 decrypts the input one-sign-bit ciphertext. and the private key of the corresponding homomorphic encryption key pair bits Perform the following decryption operation:

[0012] in, For LWE ciphertext modulus, The decrypted bit value; By comparison Compared with the preset first threshold Second threshold The size relationship determines the final plaintext symbol bit: like If so, the plaintext symbol bit is determined to be 0; like If so, the plaintext symbol bit is determined to be 1.

[0013] Furthermore, the specific steps of step S3 are as follows: S31. The service provider retrieves the stored encrypted data from the database. ; S32. The service provider uses the TFHE homomorphic encryption algorithm to perform homomorphic addition operations to compute the ciphertext data. With lower limit ciphertext First ciphertext difference :

[0014] in, This indicates a homomorphic negation operation on the lower bound ciphertext; S33. The service provider uses the TFHE homomorphic encryption algorithm to perform homomorphic addition operations to compute the upper bound ciphertext. With encrypted data Second ciphertext difference:

[0015] in, This indicates a homomorphic negation operation performed on the encrypted data. S34. Determine whether the sensitive data is an integer or a floating-point number; If the value is an integer, a carry-fill bit is added to the homomorphic addition operation; If it is a floating-point number, then sign determination, exponent alignment and mantissa difference calculation are performed in the ciphertext field according to the IEEE 754 standard; S35. The service provider obtains the first ciphertext difference. Extract the highest-order ciphertext representing the sign bit, and use it as the first sign bit ciphertext. :

[0016] S36. The service provider obtains the second ciphertext difference. Extract the highest-order ciphertext representing the sign bit, and use it as the second sign bit ciphertext. :

[0017] in, This indicates the ciphertext corresponding to the highest bit of the ciphertext. Under the two's complement rule, this bit is 0 to represent a non-negative difference and 1 to represent a negative difference.

[0018] Furthermore, in step S34, when the sensitive data is an IEEE 754 single-precision floating-point number, the specific steps for calculating the first ciphertext difference and the second ciphertext difference are as follows: S341. The service provider extracts the ciphertext data from the ciphertext domain. Lower limit ciphertext and the upper limit ciphertext The sign bit, exponent bit, and mantissa bit are represented in the ciphertext; for each ciphertext, the corresponding floating-point value is represented as... ; in, For the sign bit, An 8-digit exponent. The mantissa is 23 digits; S342. The service provider performs exponent alignment operations in the encrypted domain: Extract the encrypted data separately and lower limit ciphertext The index ciphertext and And compare the magnitudes of the exponent values ​​represented by the two; The mantissa ciphertext corresponding to the ciphertext with the smaller exponent is right-shifted by the number of bits equal to the absolute value of the difference between the two exponents. Add the same difference to the ciphertext with the smaller exponent, so that the two ciphertexts have the same exponent value; Upper limit ciphertext With encrypted data Subtraction operations perform the same exponent alignment process; S343. After exponent alignment, the service provider performs a mantissa subtraction operation in the ciphertext field based on the aligned sign bit and mantissa, and processes the special values ​​of NaN and Inf in the ciphertext field according to the IEEE 754 rules. S344. The service provider normalizes the result after subtraction to obtain a ciphertext difference result conforming to the IEEE 754 single-precision format.

[0019] Furthermore, the specific steps of step S4 are as follows: S41. The service provider will cipher the first symbol bit. Second symbol bit ciphertext Input to the input layer of the Boolean confusion circuit; S42. The decryption layer of the Boolean obfuscation circuit ciphers the first symbol bit. Second symbol bit ciphertext Perform LWE single-bit decryption separately to obtain the first plaintext symbol bit. Second plaintext symbol bit ; S43. The OR gate in the logic operation layer of a Boolean confusing circuit pairs the first plaintext sign bit. Second plaintext symbol bit Perform an OR operation to obtain the original judgment result. ,in, Plaintext representing sensitive data Plain text indicating the lower limit of the range. The plaintext representing the upper limit of the range; the truth table is: like =0, =0, then =0 means ; like =0, =1, then =1 indicates ; like =1, =0, then =1 indicates ; like =1, =1, then =1 indicates Exceeding the range; S44. The output layer of the Boolean confusion circuit will display the original decision result. The mapping is assigned to a unique Boolean decision label as the obfuscation value; S45. The service provider returns the obfuscation value to the user.

[0020] Furthermore, the specific steps of step S5 are as follows: S51. The user receives the obfuscated value returned by the service provider; S52. The user side uses the public key of the obfuscated circuit key pair. The obfuscated value is decrypted using an obfuscated circuit to obtain the plaintext determination result. ,in It can be 0 or 1; S53. The user determines the evaluation conclusion based on the plaintext judgment result: like =0, then sensitive data is determined. Located in the value range Inside; like =1, then sensitive data is determined. Not in the range Inside.

[0021] Secondly, embodiments of this application also provide an encrypted value range evaluation system based on ciphertext operations, including a user and a service provider; The users include: The key generation module is used to generate homomorphic encryption key pairs and obfuscated circuit key pairs; The data encryption module is used to encrypt sensitive data, the lower limit of the value range, and the upper limit of the value range using the public key in the homomorphic encryption key pair, respectively, to obtain data ciphertext, lower limit ciphertext, and upper limit ciphertext, and pre-sends the data ciphertext to the service provider for storage; The obfuscation circuit construction module is used to construct a Boolean obfuscation circuit for decrypting the symbol bits and performing logical operations based on the private key in the obfuscation circuit key pair and the homomorphic decryption algorithm, and send the lower limit ciphertext, the upper limit ciphertext, and the Boolean obfuscation circuit to the service provider; The result decryption module is used to receive the obfuscated value returned by the service provider, and decrypt the obfuscated value using the public key in the obfuscated circuit key pair to obtain the final evaluation result of whether the sensitive data is within the value range; Service providers include: The encrypted storage module is used to receive and store encrypted data sent by the user. The ciphertext difference calculation module is used to obtain the stored ciphertext data, and use the homomorphic encryption algorithm to calculate the first ciphertext difference between the data ciphertext and the lower limit ciphertext, and the second ciphertext difference between the upper limit ciphertext and the data ciphertext. The sign bit extraction module is used to extract the ciphertext corresponding to the sign bit from the first ciphertext difference and the second ciphertext difference, respectively, as the first sign bit ciphertext and the second sign bit ciphertext; The obfuscation circuit execution module is used to input the first symbol bit ciphertext and the second symbol bit ciphertext into the Boolean obfuscation circuit for operation, obtain the obfuscated value representing the evaluation result, and return the obfuscated value to the user.

[0022] As can be seen from the above technical solutions, this application has the following advantages: The encrypted value range evaluation method and system based on ciphertext operation provided in this application achieves efficient and accurate value range evaluation of encrypted data while ensuring the privacy and security of cloud data. This is achieved by deeply integrating homomorphic encryption and obfuscation circuits, extracting the sign bit of numerical operation in the ciphertext state and combining it with lightweight obfuscation circuits for logical judgment. This solves the problems of high computational overhead, low accuracy, or insufficient privacy protection in existing technologies for ciphertext comparison. Attached Figure Description

[0023] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating the encrypted value range evaluation method based on ciphertext operations according to the present invention.

[0025] Figure 2 This is a schematic diagram of the encrypted value range evaluation system based on ciphertext operation according to the present invention. Detailed Implementation

[0026] The various embodiments of this disclosure will be described more fully in the detailed steps of the encrypted value range evaluation method based on ciphertext operations described below. This disclosure may have various embodiments, and adjustments and changes may be made therein. However, it should be understood that there is no intention to limit the various embodiments of this disclosure to the specific embodiments disclosed herein, but rather this disclosure should be understood to cover all adjustments, equivalents, and / or alternatives falling within the spirit and scope of the various embodiments of this disclosure.

[0027] This embodiment provides a method for evaluating the range of encrypted values ​​based on ciphertext operations. By combining homomorphic and obfuscated circuits, it achieves efficient and secure range evaluation of encrypted data.

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Please see Figure 1 The diagram shows a flowchart of a method for evaluating the range of encrypted values ​​based on ciphertext operations in a specific embodiment. The method includes the following steps: S1. The user generates a homomorphic encryption key pair and a scrambling circuit key pair. The user uses the public key in the homomorphic encryption key pair to encrypt the sensitive data, the lower limit of the value range, and the upper limit of the value range, respectively, to obtain the data ciphertext, the lower limit ciphertext, and the upper limit ciphertext. The data ciphertext is then sent to the service provider for storage in advance. It should be noted that this step establishes a secure communication foundation. By having the user control the private key, data sovereignty is ensured. Sensitive data and thresholds are encrypted with the public key, allowing the service provider to perform operations on the ciphertext without knowing the plaintext. The ciphertext is pre-stored by the service provider, achieving separation of computation and storage. S2. The user constructs a Boolean obfuscation circuit for decrypting the symbol bits and performing logical operations based on the private key in the obfuscation circuit key pair and the homomorphic decryption algorithm, and sends the lower limit ciphertext, the upper limit ciphertext, and the Boolean obfuscation circuit to the service provider. It should be noted that this step achieves the separation of logic and data. The user sends the obfuscated circuit containing the decryption logic to the service provider, enabling the service provider to assist in completing part of the decryption and logical judgment without accessing the private key. This avoids the service provider directly accessing the plaintext and also reduces the user's online participation time. S3. The service provider obtains the stored encrypted data, uses a homomorphic encryption algorithm to calculate the first ciphertext difference between the encrypted data and the lower bound ciphertext, and the second ciphertext difference between the upper bound ciphertext and the encrypted data, and extracts the ciphertext corresponding to the sign bit from the first ciphertext difference and the second ciphertext difference, respectively, as the first sign bit ciphertext and the second sign bit ciphertext. It should be noted that by calculating the difference between the data and the lower limit and the upper limit and the data through homomorphic operations, and only extracting the sign bit of the result as ciphertext, compared to completely decrypting the entire value or building a complex comparison circuit, extracting the sign bit reduces the amount of data that needs to be transmitted and processed, and the sign bit is sufficient to determine the positive or negative value, thereby greatly improving the computational efficiency. S4. The service provider inputs the first symbol bit ciphertext and the second symbol bit ciphertext into the Boolean obfuscation circuit to run, obtains the obfuscated value representing the evaluation result, and returns it to the user. It should be noted that this step uses a scrambling circuit to decrypt the ciphertext of the symbol bits and perform logical operations. Since the scrambling circuit has been constructed and encrypted by the user, the service provider cannot know the internal private key information when running the circuit, but can obtain the correct logical result. Thus, under the premise of ensuring security, the service provider's computing power completes the complex logical judgment. S5. The user uses the public key in the obfuscated circuit key pair to decrypt the obfuscated value and obtain the final evaluation result of whether the sensitive data is within the value range; It should be noted that this step completes the closed loop of privacy computation. The user uses the public key to decrypt and obtain the final result, confirming whether the data is within the set value range. Throughout the entire process, the user does not need to expose the data in plaintext to the service provider, and the service provider does not need to expose the data to the user, thus achieving two-way privacy protection.

[0030] This embodiment calculates the sign bit of the difference using TFHE homomorphic computation and performs logic decryption using a scrambling circuit, achieving efficient range checking of data without the need for decryption, thus balancing security and computational efficiency.

[0031] Furthermore, as a refinement and extension of the specific implementation of the above embodiments, in order to fully illustrate the specific implementation process in this embodiment, another method for evaluating the encrypted value range based on ciphertext operations is provided. This method includes the following steps: S1. The user generates a homomorphic encryption key pair and a scrambling circuit key pair. The user uses the public key in the homomorphic encryption key pair to encrypt the sensitive data, the lower limit of the value range, and the upper limit of the value range, respectively, to obtain the data ciphertext, the lower limit ciphertext, and the upper limit ciphertext. The data ciphertext is then sent to the service provider for storage in advance. The specific steps of step S1 are as follows: S11. The user runs the key generation function of the TFHE homomorphic encryption algorithm to generate homomorphic encryption key pairs:

[0032] in, The private key for a homomorphic encryption key pair. The public key of the homomorphic encryption key pair; S12. The user runs the key generation function of the obfuscation circuit to generate obfuscation circuit key pairs:

[0033] in, To obfuscate the private key of the circuit key pair The public key for the obfuscated circuit key pair; S13. The user side represents sensitive data, lower limit of value range, and upper limit of value range as binary bit sequences respectively; among them, integers are encoded using binary two's complement and the most significant bit is reserved as the sign bit, and floating-point numbers are encoded using the IEEE 754 single-precision standard; S14. The public key of the homomorphic encryption key pair used by the user. Perform homomorphic encryption on each bit of the binary bit sequence containing the sensitive data, the lower limit of the value range, and the upper limit of the value range to obtain the ciphertext. Lower limit ciphertext and the upper limit ciphertext ; The specific steps of step S14 are as follows: S141. The user takes sensitive data, lower limit of value range and upper limit of value range as data to be encrypted, and obtains the binary bit sequence of the data to be encrypted. The length of the binary bit sequence is L. For integer data, the binary bit sequence includes the most significant bit as the sign bit and the subsequent value bits. S142. The user extends the least significant bit of the binary bit sequence by one padding bit to obtain an extended bit sequence of length L+1; the plaintext value of the padding bit is 0. S143. The user uses the public key of the homomorphic encryption key pair. Each bit in the extended bit sequence is independently encrypted using LWE to generate the corresponding independent bit ciphertext, thus obtaining a ciphertext sequence containing L+1 bit ciphertext, where the ciphertext corresponding to the padding bit is the padding bit ciphertext. S144. The user ciphers the data corresponding to the sensitive data in the ciphertext sequence. The lower limit ciphertext corresponding to the lower limit of the value range Or the upper limit ciphertext corresponding to the upper limit of the value range Output; The padding ciphertext is used to store carry information from the lower-order numerical bits when the service provider performs homomorphic addition in the subsequent step S3, so as to avoid carry overflow to the sign bit. In this embodiment, the padding bit added in step S142 is located after the least significant bit of the binary bit sequence. When the service provider performs homomorphic addition in step S32 or S33, the addition of the least significant bits of the two ciphertexts may produce a carry, which will be stored in the ciphertext corresponding to the padding bit. For example, for integer two's complement representation, if both least significant bits are 1, their sum is 0 with a carry of 1. The padding bit ciphertext records this carry to ensure the correctness of subsequent high-bit operations. Since the padding bit is located at the farthest end after the sign bit, the carry propagates to the padding bit at most before being absorbed, and will not affect the accuracy of the sign bit. After all homomorphic additions are completed, the final value of the padding bit can be ignored and does not need to be decrypted. This mechanism avoids carry overflow errors caused by insufficient bit width in traditional homomorphic addition and ensures the correctness of subsequent sign bit extraction. S15. The user will encrypt the data. Pre-sent to the service provider's storage; S2. The user constructs a Boolean obfuscation circuit for decrypting the symbol bits and performing logical operations based on the private key in the obfuscation circuit key pair and the homomorphic decryption algorithm, and sends the lower limit ciphertext, the upper limit ciphertext, and the Boolean obfuscation circuit to the service provider. The specific steps of step S2 are as follows: S21. The user constructs a private key based on the homomorphic decryption algorithm, which only accepts single-bit symbolic ciphertext and homomorphic encryption key pairs. Each bit is used as the input layer; S22. The user side constructs a decryption layer based on the LWE single-bit decryption gate circuit to decrypt the two-sign-bit ciphertext input to obtain two plaintext sign bits; The LWE single-bit decryption gate circuit in step S22 is used to cipher the input one sign bit. and the private key of the corresponding homomorphic encryption key pair bits Perform the following decryption operation:

[0034] in, For LWE ciphertext modulus, The decrypted bit value; By comparison Compared with the preset first threshold Second threshold The size relationship determines the final plaintext symbol bit: like If so, the plaintext symbol bit is determined to be 0; like If so, the plaintext symbol bit is determined to be 1; S23. The user constructs a logic operation layer, which has a built-in OR gate for performing an OR logic operation on the two plaintext symbol bits obtained by decryption; S24. The user constructs an output layer to map the output of the OR gate to a Boolean decision label as an obfuscation value; S25. The user uses the public key of the obfuscated circuit key pair. All gate circuits in the input layer, decryption layer, logic operation layer, and output layer are encrypted and scrambled to generate the final Boolean obfuscated circuit; S26. The user will send the lower limit ciphertext. Upper limit ciphertext And Boolean confusing circuitry sent to the service provider; S3. The service provider obtains the stored encrypted data, uses a homomorphic encryption algorithm to calculate the first ciphertext difference between the encrypted data and the lower bound ciphertext, and the second ciphertext difference between the upper bound ciphertext and the encrypted data, and extracts the ciphertext corresponding to the sign bit from the first ciphertext difference and the second ciphertext difference, respectively, as the first sign bit ciphertext and the second sign bit ciphertext. The specific steps of step S3 are as follows: S31. The service provider retrieves the stored encrypted data from the database. ; S32. The service provider uses the TFHE homomorphic encryption algorithm to perform homomorphic addition operations to compute the ciphertext data. With lower limit ciphertext First ciphertext difference :

[0035] in, This indicates a homomorphic negation operation on the lower bound ciphertext; S33. The service provider uses the TFHE homomorphic encryption algorithm to perform homomorphic addition operations to compute the upper bound ciphertext. With encrypted data Second ciphertext difference:

[0036] in, This indicates a homomorphic negation operation performed on the encrypted data. S34. Determine whether the sensitive data is an integer or a floating-point number; If the value is an integer, a carry-fill bit is added to the homomorphic addition operation; If it is a floating-point number, then sign determination, exponent alignment and mantissa difference calculation are performed in the ciphertext field according to the IEEE 754 standard; In step S34, when the sensitive data is an IEEE 754 single-precision floating-point number, the specific steps for calculating the first ciphertext difference and the second ciphertext difference are as follows: S341. The service provider extracts the ciphertext data from the ciphertext domain. Lower limit ciphertext and the upper limit ciphertext The sign bit, exponent bit, and mantissa bit are represented in the ciphertext; for each ciphertext, the corresponding floating-point value is represented as... ; in, For the sign bit, An 8-digit exponent. The mantissa is 23 digits; S342. The service provider performs exponent alignment operations in the encrypted domain: Extract the encrypted data separately and lower limit ciphertext The index ciphertext and And compare the magnitudes of the exponent values ​​represented by the two; The mantissa ciphertext corresponding to the ciphertext with the smaller exponent is right-shifted by the number of bits equal to the absolute value of the difference between the two exponents. Add the same difference to the ciphertext with the smaller exponent (i.e., align it to the larger exponent) so that the two ciphertexts have the same exponent value. Upper limit ciphertext With encrypted data Subtraction operations perform the same exponent alignment process; S343. After exponent alignment, the service provider performs a mantissa subtraction operation in the ciphertext field based on the aligned sign bit and mantissa, and handles the special values ​​NaN and Inf in the ciphertext field according to IEEE 754 rules: If the data is encrypted Lower limit ciphertext Or upper limit ciphertext If any ciphertext represents NaN (i.e., not a number), then return directly: not within the range, and terminate the current difference calculation; If the data is encrypted Lower limit ciphertext Or upper limit ciphertext If any ciphertext represents infinity (i.e., Inf), then according to the IEEE 754 rules: Subtracting any finite number from positive infinity results in positive infinity, subtracting negative infinity results in negative infinity, and subtracting two infinitys results in NaN, all of which are considered to be outside the interval. For non-special values, perform mantissa subtraction in the ciphertext field based on the aligned sign bit and mantissa (i.e., ...). or ), and handle borrowing; S344. The service provider normalizes the result after subtraction to obtain a ciphertext difference result that conforms to the IEEE 754 single-precision format; Specifically as follows: Check if the highest bit of the ciphertext of the mantissa of the subtraction result is 1 (i.e., whether it is within the normalization range). If the mantissa has a leading zero, shift the mantissa to the left and decrease the value of the exponent ciphertext accordingly until the highest bit of the mantissa is 1 or the exponent reaches the minimum value. If the subtraction result is 0, then the exponent ciphertext is set to 0, the mantissa ciphertext is set to 0, and the sign bit ciphertext is set to 0 (indicating positive zero). Finally, the first ciphertext difference result conforming to the IEEE 754 single-precision format is obtained. Difference between the second ciphertext ; The specific applications of handling special values ​​of NaN and Inf in step S343 in different scenarios are as follows: Scenario 1 including NaN, assuming sensitive data =NaN, lower limit =10.0; Service provider extracts encrypted data The NaN code is defined with all exponent bits set to 1 and the mantissa bits set to non-zero; in this case, regardless of the calculation... still All of them directly return the preset flag that is not in the range (that is, the obfuscation value corresponding to the flag can be pre-defined in the output layer of the obfuscation circuit), without needing to perform subsequent mantissa subtraction; Scenario 2 containing positive infinity: Let =+∞, =100.0; encrypted data The exponent bits are all 1s, the mantissa bits are all 0s, and the sign bit is 0 (i.e., positive infinity); Calculate At that time, according to the IEEE 754 rule, positive infinity minus any finite number still equals positive infinity, therefore the first ciphertext difference is still represented as positive infinity; similarly, if If the number is finite, then The value is negative infinity; at this time, the sign bit corresponding to positive infinity is 0 (i.e., non-negative), and the sign bit corresponding to negative infinity is 1 (i.e., negative). However, according to the interval judgment logic of this application, as long as... If it is infinite, it is considered to be outside any finite interval, so in the special value determination stage, it is directly returned that it is not in the interval; Scenario 3: Subtracting infinity from infinity: Let =+∞, =+∞; at this time If the value is NaN, it will also return that the value is not within the range. By using the above special value determination, we ensure that the floating-point number evaluation results conform to the semantics of the IEEE 754 standard and do not disclose any plaintext information. S35. The service provider obtains the first ciphertext difference. Extract the highest-order ciphertext representing the sign bit, and use it as the first sign bit ciphertext. :

[0037] S36. The service provider obtains the second ciphertext difference. Extract the highest-order ciphertext representing the sign bit, and use it as the second sign bit ciphertext. :

[0038] in, This indicates the ciphertext corresponding to the highest bit of the ciphertext. Under the two's complement rule, this bit is 0 to represent a non-negative difference and 1 to represent a negative difference. S4. The service provider inputs the first symbol bit ciphertext and the second symbol bit ciphertext into the Boolean obfuscation circuit to run, obtains the obfuscated value representing the evaluation result, and returns it to the user. The specific steps of step S4 are as follows: S41. The service provider will cipher the first symbol bit. Second symbol bit ciphertext Input to the input layer of the Boolean confusion circuit; S42. The decryption layer of the Boolean obfuscation circuit ciphers the first symbol bit. Second symbol bit ciphertext Perform LWE single-bit decryption separately to obtain the first plaintext symbol bit. Second plaintext symbol bit ; S43. The OR gate in the logic operation layer of a Boolean confusing circuit pairs the first plaintext sign bit. Second plaintext symbol bit Perform an OR operation to obtain the original judgment result. ,in, Plaintext representing sensitive data Plain text indicating the lower limit of the range. The plaintext representing the upper limit of the range; the truth table is: like =0, =0, then =0 means ; like =0, =1, then =1 indicates ; like =1, =0, then =1 indicates ; like =1, =1, then =1 indicates Exceeding the range; S44. The output layer of the Boolean confusion circuit will display the original decision result. The mapping is assigned to a unique Boolean decision label as the obfuscation value; S45. The service provider returns the obfuscated value to the user. S5. The user uses the public key in the obfuscated circuit key pair to decrypt the obfuscated value and obtain the final evaluation result of whether the sensitive data is within the value range; The specific steps of step S5 are as follows: S51. The user receives the obfuscated value returned by the service provider; S52. The user side uses the public key of the obfuscated circuit key pair. The obfuscated value is decrypted using an obfuscated circuit to obtain the plaintext determination result. ,in It can be 0 or 1; S53. The user determines the evaluation conclusion based on the plaintext judgment result: like =0, then sensitive data is determined. Located in the value range Inside; like =1, then sensitive data is determined. Not in the range Inside.

[0039] In an example of evaluation over an integer value range, suppose a user bank needs to determine the amount of a transaction. Is 50 (i.e., an integer) within the compliant range? =30, =80] within. The service provider's cloud server has pre-stored encrypted data. .

[0040] Execution key generation and encryption: User side operation Generate homomorphic encryption key pairs ,run Generate obfuscated circuit key pairs .

[0041] Taking 8-bit representation as an example, =50、 =30、 =80 is converted to its two's complement sequence: =00110010, =00011110, =01010000.

[0042] Extend each sequence by one padding bit (i.e., plaintext 0) after its least significant bit, resulting in a 9-bit extended sequence. Use Each bit is encrypted independently, resulting in , , The user will Send to the service provider's storage.

[0043] Constructing a confusing circuit: The user constructs an obfuscation circuit based on the TFHE decryption algorithm, which only receives a single-bit symbol ciphertext and the TFHE private key bit; this circuit includes: an input layer (receiving two symbol bits of ciphertext). , The system consists of a decryption layer (two LWE single-bit decryption gates), a logic operation layer (an OR gate), and an output layer (which maps the OR gate output to a 32-bit random string as an obfuscation value). The user side uses... After scrambling the encryption, , The obfuscated circuit is then sent to the service provider.

[0044] Perform ciphertext difference calculation: Service provider acquisition ,calculate:

[0045]

[0046] Since the result is an integer, padding bits are used to store the carry during homomorphic addition, and the result is still a 9-bit ciphertext sequence.

[0047] Extract the sign bit ciphertext: from Extract the highest-order ciphertext from (i.e., 50-30). Since 20 is a positive number, the highest-order plaintext is 0. =0 ciphertext.

[0048] from Extract the highest-order ciphertext from (i.e., 80-50). =0 ciphertext.

[0049] Running the confusion circuit: The service provider will , Input obfuscation circuit. The decryption layer uses the embedded TFHE private key to perform LWE decryption on the two symbol bits of the ciphertext, respectively, to obtain the plaintext symbol bits. =0, =0. OR gate output. =0. The output layer will =0 is mapped to an obfuscated value (e.g., 0x7F3A...). The service provider returns this obfuscated value to the user.

[0050] Decryption result obtained: User side uses Decrypt the obfuscated value to obtain =0, indicating that 50 is within [30,80].

[0051] like =90, then The sign bit is 0. The sign bit is 1 (negative). The obfuscated circuit is decrypted. =0, =1, retrieved from the truth table =1, and after the user decrypts, they find that 90 is not in the interval [30,80].

[0052] In another specific embodiment of evaluating floating-point monetary values, set up =12.5, =10.0, =15.0, all are IEEE 754 single-precision floating-point numbers. The same key generation and encryption process as the above embodiment is used, but the encoding follows the IEEE 754 standard: The binary representation of 12.5 is: 0 10000010 100100000000000000000000 (sign bit 0, exponent 130-127=3, mantissa 1.5625).

[0053] The binary representation of 10.0 is: 0 10000010 010000000000000000000000.

[0054] The binary representation of 15.0 is: 0 10000011 11100000000000000000000.

[0055] Perform ciphertext difference calculation: Service provider calculation : Extraction Index: =130, =130, the exponents are equal, no alignment is needed.

[0056] Subtracting the last digits: 1.5625 - 1.25 = 0.3125, corresponding to the ciphertext of the last digits. .

[0057] With all sign bits set to 0, the difference is positive, and the result after normalization remains the same. This corresponds to the ciphertext of a floating-point number of 2.5.

[0058] calculate : Extraction Index: =131, =130, exponent difference 1, will the smaller exponent ( ) is shifted one bit to the right and its exponent is increased to 131. After alignment, the mantissas are subtracted to obtain the ciphertext 2.5.

[0059] Perform sign bit extraction: The sign bit is 0. The sign bit is 0, therefore =0 ciphertext, =0 ciphertext.

[0060] Obfuscated circuit operation and decryption: Similar to the previous embodiment, the following is obtained: =0, determine 12.5∈[10.0,15.0].

[0061] Special value test: If =NaN. If the service provider detects the NaN flag before calculating the difference, it will directly return a pre-defined obfuscated value that is not within the range and will not perform any further calculations.

[0062] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0063] like Figure 2 As shown, the following are embodiments of the encrypted value range evaluation system based on ciphertext operation provided in this disclosure. This system and the encrypted value range evaluation method based on ciphertext operation in the above embodiments belong to the same inventive concept. For details not described in detail in the embodiments of the encrypted value range evaluation system based on ciphertext operation, please refer to the embodiments of the encrypted value range evaluation method based on ciphertext operation described above.

[0064] The system includes users and service providers; The users include: The key generation module is used to generate homomorphic encryption key pairs and obfuscated circuit key pairs; The data encryption module is used to encrypt sensitive data, the lower limit of the value range, and the upper limit of the value range using the public key in the homomorphic encryption key pair, respectively, to obtain data ciphertext, lower limit ciphertext, and upper limit ciphertext, and pre-sends the data ciphertext to the service provider for storage; The obfuscation circuit construction module is used to construct a Boolean obfuscation circuit for decrypting the symbol bits and performing logical operations based on the private key in the obfuscation circuit key pair and the homomorphic decryption algorithm, and send the lower limit ciphertext, the upper limit ciphertext, and the Boolean obfuscation circuit to the service provider; The result decryption module is used to receive the obfuscated value returned by the service provider, and decrypt the obfuscated value using the public key in the obfuscated circuit key pair to obtain the final evaluation result of whether the sensitive data is within the value range; Service providers include: The encrypted storage module is used to receive and store encrypted data sent by the user. The ciphertext difference calculation module is used to obtain the stored ciphertext data, and use the homomorphic encryption algorithm to calculate the first ciphertext difference between the data ciphertext and the lower limit ciphertext, and the second ciphertext difference between the upper limit ciphertext and the data ciphertext. The sign bit extraction module is used to extract the ciphertext corresponding to the sign bit from the first ciphertext difference and the second ciphertext difference, respectively, as the first sign bit ciphertext and the second sign bit ciphertext; The obfuscation circuit execution module is used to input the first symbol bit ciphertext and the second symbol bit ciphertext into the Boolean obfuscation circuit for operation, obtain the obfuscated value representing the evaluation result, and return the obfuscated value to the user.

[0065] This embodiment achieves efficient and accurate value range assessment and privacy protection determination of cloud-encrypted data by means of the interactive collaboration of the key generation module, data encryption module, obfuscation circuit construction module, result decryption module, ciphertext storage module, ciphertext difference calculation module, sign bit extraction module, and obfuscation circuit execution module, while ensuring that sensitive data is not leaked throughout the process.

[0066] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for evaluating the range of encrypted values ​​based on ciphertext operations, characterized in that, Includes the following steps: S1. The user generates a homomorphic encryption key pair and a scrambling circuit key pair. The user uses the public key in the homomorphic encryption key pair to encrypt the sensitive data, the lower limit of the value range, and the upper limit of the value range, respectively, to obtain the data ciphertext, the lower limit ciphertext, and the upper limit ciphertext. The data ciphertext is then sent to the service provider for storage in advance. S2. The user constructs a Boolean obfuscation circuit for decrypting the symbol bits and performing logical operations based on the private key in the obfuscation circuit key pair and the homomorphic decryption algorithm, and sends the lower limit ciphertext, the upper limit ciphertext, and the Boolean obfuscation circuit to the service provider. S3. The service provider obtains the stored encrypted data, uses a homomorphic encryption algorithm to calculate the first ciphertext difference between the encrypted data and the lower bound ciphertext, and the second ciphertext difference between the upper bound ciphertext and the encrypted data, and extracts the ciphertext corresponding to the sign bit from the first ciphertext difference and the second ciphertext difference, respectively, as the first sign bit ciphertext and the second sign bit ciphertext. S4. The service provider inputs the first symbol bit ciphertext and the second symbol bit ciphertext into the Boolean obfuscation circuit to run, obtains the obfuscated value representing the evaluation result, and returns it to the user. S5. The user uses the public key in the obfuscated circuit key pair to decrypt the obfuscated value and obtain the final evaluation result of whether the sensitive data is within the value range.

2. The method for evaluating the range of encrypted values ​​based on ciphertext operations according to claim 1, characterized in that, The specific steps of step S1 are as follows: S11. The user runs the key generation function of the TFHE homomorphic encryption algorithm to generate homomorphic encryption key pairs: in, The private key for a homomorphic encryption key pair. The public key of the homomorphic encryption key pair; S12. The user runs the key generation function of the obfuscation circuit to generate obfuscation circuit key pairs: in, To obfuscate the private key of the circuit key pair The public key for the obfuscated circuit key pair; S13. The user side represents sensitive data, lower limit of value range, and upper limit of value range as binary bit sequences respectively; among them, integers are encoded using binary two's complement and the most significant bit is reserved as the sign bit, and floating-point numbers are encoded using the IEEE 754 single-precision standard; S14. The public key of the homomorphic encryption key pair used by the user. Perform homomorphic encryption on each bit of the binary bit sequence containing the sensitive data, the lower limit of the value range, and the upper limit of the value range to obtain the ciphertext. Lower limit ciphertext and the upper limit ciphertext ; S15. The user will encrypt the data. It is sent in advance to the service provider's storage.

3. The method for evaluating the range of encrypted values ​​based on ciphertext operations according to claim 2, characterized in that, The specific steps of step S14 are as follows: S141. The user takes sensitive data, lower limit of value range and upper limit of value range as data to be encrypted, and obtains the binary bit sequence of the data to be encrypted. The length of the binary bit sequence is L. For integer data, the binary bit sequence includes the most significant bit as the sign bit and the subsequent value bits. S142. The user extends the least significant bit of the binary bit sequence by one padding bit to obtain an extended bit sequence of length L+1; the plaintext value of the padding bit is 0. S143. The user uses the public key of the homomorphic encryption key pair. Each bit in the extended bit sequence is independently encrypted using LWE to generate the corresponding independent bit ciphertext, thus obtaining a ciphertext sequence containing L+1 bit ciphertext, where the ciphertext corresponding to the padding bit is the padding bit ciphertext. S144. The user ciphers the data corresponding to the sensitive data in the ciphertext sequence. The lower limit ciphertext corresponding to the lower limit of the value range Or the upper limit ciphertext corresponding to the upper limit of the value range Output.

4. The method for evaluating the range of encrypted values ​​based on ciphertext operations according to claim 3, characterized in that, The specific steps of step S2 are as follows: S21. The user constructs a private key based on the homomorphic decryption algorithm, which only accepts single-bit symbolic ciphertext and homomorphic encryption key pairs. Each bit is used as the input layer; S22. The user side constructs a decryption layer based on the LWE single-bit decryption gate circuit to decrypt the two-sign-bit ciphertext input to obtain two plaintext sign bits; S23. The user constructs a logic operation layer, which has a built-in OR gate for performing an OR logic operation on the two plaintext symbol bits obtained by decryption; S24. The user constructs an output layer to map the output of the OR gate to a Boolean decision label as an obfuscation value; S25. The user uses the public key of the obfuscated circuit key pair. All gate circuits in the input layer, decryption layer, logic operation layer, and output layer are encrypted and scrambled to generate the final Boolean obfuscated circuit; S26. The user will send the lower limit ciphertext. Upper limit ciphertext And Boolean confusing circuitry sent to the service provider.

5. The method for evaluating the range of encrypted values ​​based on ciphertext operations according to claim 4, characterized in that, The LWE single-bit decryption gate circuit in step S22 is used to cipher the input one sign bit. and the private key of the corresponding homomorphic encryption key pair bits Perform the following decryption operation: in, For LWE ciphertext modulus, The decrypted bit value; By comparison Compared with the preset first threshold Second threshold The size relationship determines the final plaintext symbol bit: like If so, the plaintext symbol bit is determined to be 0; like If so, the plaintext symbol bit is determined to be 1.

6. The method for evaluating the range of encrypted values ​​based on ciphertext operations according to claim 4, characterized in that, The specific steps of step S3 are as follows: S31. The service provider retrieves the stored encrypted data from the database. ; S32. The service provider uses the TFHE homomorphic encryption algorithm to perform homomorphic addition operations to compute the ciphertext data. With lower limit ciphertext First ciphertext difference : in, This indicates a homomorphic negation operation on the lower bound ciphertext; S33. The service provider uses the TFHE homomorphic encryption algorithm to perform homomorphic addition operations to compute the upper bound ciphertext. With encrypted data Second ciphertext difference: in, This indicates a homomorphic negation operation performed on the encrypted data. S34. Determine whether the sensitive data is an integer or a floating-point number; If the value is an integer, a carry-fill bit is added to the homomorphic addition operation; If it is a floating-point number, then sign determination, exponent alignment and mantissa difference calculation are performed in the ciphertext field according to the IEEE 754 standard; S35. The service provider obtains the first ciphertext difference. Extract the highest-order ciphertext representing the sign bit, and use it as the first sign bit ciphertext. : S36. The service provider obtains the second ciphertext difference. Extract the highest-order ciphertext representing the sign bit, and use it as the second sign bit ciphertext. : in, This indicates the ciphertext corresponding to the highest bit of the ciphertext. Under the two's complement rule, this bit is 0 to represent a non-negative difference and 1 to represent a negative difference.

7. The method for evaluating the range of encrypted values ​​based on ciphertext operations according to claim 6, characterized in that, In step S34, when the sensitive data is an IEEE 754 single-precision floating-point number, the specific steps for calculating the first ciphertext difference and the second ciphertext difference are as follows: S341. The service provider extracts the ciphertext data from the ciphertext domain. Lower limit ciphertext and the upper limit ciphertext The sign bit, exponent bit, and mantissa bit are represented in the ciphertext; for each ciphertext, the corresponding floating-point value is represented as... ; in, For the sign bit, An 8-digit exponent. The mantissa is 23 digits; S342. The service provider performs exponent alignment operations in the encrypted domain: Extract the encrypted data separately and lower limit ciphertext The index ciphertext and And compare the magnitudes of the exponent values ​​represented by the two; The mantissa ciphertext corresponding to the ciphertext with the smaller exponent is right-shifted by the number of bits equal to the absolute value of the difference between the two exponents. Add the same difference to the ciphertext with the smaller exponent, so that the two ciphertexts have the same exponent value; Upper limit ciphertext With encrypted data Subtraction operations perform the same exponent alignment process; S343. After exponent alignment, the service provider performs a mantissa subtraction operation in the ciphertext field based on the aligned sign bit and mantissa, and processes the special values ​​of NaN and Inf in the ciphertext field according to the IEEE 754 rules. S344. The service provider normalizes the result after subtraction to obtain a ciphertext difference result conforming to the IEEE 754 single-precision format.

8. The method for evaluating the range of encrypted values ​​based on ciphertext operations according to claim 6, characterized in that, The specific steps of step S4 are as follows: S41. The service provider will cipher the first symbol bit. Second symbol bit ciphertext Input to the input layer of the Boolean confusion circuit; S42. The decryption layer of the Boolean obfuscation circuit ciphers the first symbol bit. Second symbol bit ciphertext Perform LWE single-bit decryption separately to obtain the first plaintext symbol bit. Second plaintext symbol bit ; S43. The OR gate in the logic operation layer of a Boolean confusing circuit pairs the first plaintext sign bit. Second plaintext symbol bit Perform an OR operation to obtain the original judgment result. ,in, Plaintext representing sensitive data Plain text indicating the lower limit of the range. The plaintext representing the upper limit of the range; the truth table is: like =0, =0, then =0 means ; like =0, =1, then =1 indicates ; like =1, =0, then =1 indicates ; like =1, =1, then =1 indicates Exceeding the range; S44. The output layer of the Boolean confusion circuit will display the original decision result. The mapping is assigned to a unique Boolean decision label as the obfuscation value; S45. The service provider returns the obfuscation value to the user.

9. The method for evaluating the range of encrypted values ​​based on ciphertext operations according to claim 8, characterized in that, The specific steps of step S5 are as follows: S51. The user receives the obfuscated value returned by the service provider; S52. The user side uses the public key of the obfuscated circuit key pair. The obfuscated value is decrypted using an obfuscated circuit to obtain the plaintext determination result. ,in It can be 0 or 1; S53. The user determines the evaluation conclusion based on the plaintext judgment result: like =0, then sensitive data is determined. Located in the value range Inside; like =1, then sensitive data is determined. Not in the range Inside.

10. A system for evaluating the range of encrypted values ​​based on ciphertext operations, characterized in that, Including users and service providers; The users include: The key generation module is used to generate homomorphic encryption key pairs and obfuscated circuit key pairs; The data encryption module is used to encrypt sensitive data, the lower limit of the value range, and the upper limit of the value range using the public key in the homomorphic encryption key pair, respectively, to obtain data ciphertext, lower limit ciphertext, and upper limit ciphertext, and pre-sends the data ciphertext to the service provider for storage; The obfuscation circuit construction module is used to construct a Boolean obfuscation circuit for decrypting the symbol bits and performing logical operations based on the private key in the obfuscation circuit key pair and the homomorphic decryption algorithm, and send the lower limit ciphertext, the upper limit ciphertext, and the Boolean obfuscation circuit to the service provider; The result decryption module is used to receive the obfuscated value returned by the service provider, and decrypt the obfuscated value using the public key in the obfuscated circuit key pair to obtain the final evaluation result of whether the sensitive data is within the value range; Service providers include: The encrypted storage module is used to receive and store encrypted data sent by the user. The ciphertext difference calculation module is used to obtain the stored ciphertext data, and use the homomorphic encryption algorithm to calculate the first ciphertext difference between the data ciphertext and the lower limit ciphertext, and the second ciphertext difference between the upper limit ciphertext and the data ciphertext. The sign bit extraction module is used to extract the ciphertext corresponding to the sign bit from the first ciphertext difference and the second ciphertext difference, respectively, as the first sign bit ciphertext and the second sign bit ciphertext; The obfuscation circuit execution module is used to input the first symbol bit ciphertext and the second symbol bit ciphertext into the Boolean obfuscation circuit for operation, obtain the obfuscated value representing the evaluation result, and return the obfuscated value to the user.

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