A double encryption image protection method based on chaotic mapping and linear congruence method

Abstract

This invention discloses a dual-encryption image protection method based on chaotic mapping and linear congruence, specifically including the following steps: S1: Obtain the image to be encrypted and convert the image into a data sequence; S2: Scramble the image sequence of the data sequence using the AES encryption algorithm to obtain the first sequence to be encrypted; S3: Construct a chaotic system to generate a chaotic sequence and map and encrypt the chaotic sequence to obtain a key sequence; S4: Perform an XOR operation on the first sequence to be encrypted and the key sequence to output the encrypted sequence.

Description

Technical Field

[0001] This invention relates to the field of image processing technology, and in particular to a dual-encryption image protection method based on chaotic mapping and linear congruence method. Background Technology

[0002] With the rapid development of computer networks, the number of images transmitted over the network is increasing, raising concerns about the secure transmission of images. Currently, scholars both domestically and internationally are paying close attention to how to encrypt images during transmission. Traditional encryption methods may face risks of low security and susceptibility to external interference.

[0003] Existing technologies generally employ image encryption methods based on chaotic sequences, and existing schemes include:

[0004] The invention patent, "A Novel Eighth-Order Hyperchaotic System and Its Method for Encryption and Decryption in Images" (Application No.: 202311109735.3), encrypts images by using a complex hyperchaotic equation as a pseudo-random sequence generator to separate, scramble, and diffuse the RGB channels of the image. The decryption process is the reverse of the encryption steps, using the same sequence to reconstruct the image in reverse order, ensuring the security and effectiveness of the encryption while improving resistance to various attacks. However, due to the use of an eighth-order hyperchaotic equation, the system involves a relatively complex computational process, leading to high computational resource consumption, especially in applications requiring rapid encryption and decryption. For real-time image encryption and decryption, the system's high complexity results in processing delays, making it unsuitable for applications requiring immediate response. Implementing such a high-order hyperchaotic encryption system requires more powerful hardware to handle complex algorithms and large amounts of data operations, increasing system deployment costs.

[0005] The invention patent "A High-Dimensional Hyperchaotic Image Encryption Method Using Arnold Transform and DNA Hybrid Encoding Scrambling" (Application No.: 202311331535.2) involves converting the original image into a pixel matrix, processing these matrices using an Arnold transform and an eight-dimensional sixth-order hyperchaotic system to generate multiple intermediate matrices. These matrices are then processed using DNA encoding and computation to finally obtain the encrypted image. This method improves the complexity and security of image encryption by combining spatial scrambling of the Arnold transform with numerical scrambling of DNA encoding. However, the use of an eight-dimensional hyperchaotic system and the Arnold transform results in high computational complexity and memory consumption, making it unsuitable for applications requiring rapid processing. Integrating the Arnold transform, DNA encoding, and the hyperchaotic system requires precise parameter tuning and strict synchronization, which increases the complexity of implementation.

[0006] The invention patent, "A Compressible Six-Dimensional Non-Degenerate Hyperchaotic Image Security System and Method" (Authorization No.: 202111180734.9), first compresses image data to generate a compression coefficient matrix. Then, a six-dimensional hyperchaotic system generates a chaotic sequence to encrypt the compressed data, forming ciphertext. At the decryption end, the same hyperchaotic sequence is used to reverse the operation to restore the original compressed data, and finally, the original image is recovered through decompression. This system utilizes the high randomness of the hyperchaotic system and SOPC resources to accelerate the chaotic discretization process in parallel within an FPGA, improving the efficiency and security of the image security system. This invention relies on the high integration of the six-dimensional hyperchaotic system and SOPC, making its implementation complex and requiring a high level of expertise from technical personnel. The extensive use of FPGA and SOPC resources in the system design leads to high hardware costs and dependence on specific hardware. Although image data compression and parallel processing techniques are used, the high-dimensional hyperchaotic system itself results in high computational resource consumption. The system's operation is highly dependent on the preset hardware configuration and algorithm design, which limits its flexibility and adaptability in different application scenarios.

[0007] The invention patent "A Novel Hyperchaotic Image Encryption Method" (Authorization No.: 201610908104.1) involves three key steps: key initialization, scrambling transformation, and Hyperhenon hyperchaotic mapping diffusion. The initial key consists of a binary auxiliary key and an input key, and a hyperchaotic sequence is generated using a Hyperhenon mapping for diffusion operations. The image is first segmented into multiple column vector groups, bit-ified, and then scrambled using an Arnold mapping to generate intermediate ciphertext. Then, the hyperchaotic sequence is used in a diffusion operation with the intermediate ciphertext to generate the final ciphertext. This method effectively improves the security of image encryption and resists statistical feature attacks and differential attacks. This encryption method involves multiple steps, including bit-ification processing, scrambling operations, and chaotic sequence generation, each requiring precise calculation and control, making it complex to implement. Due to the use of high-dimensional chaotic mapping and multiple iterative operations, this leads to high computational overhead, affecting the speed of encryption and decryption, especially when processing large-scale image data. The high computational requirements may require strong hardware support, increasing implementation costs, especially when deployed on resource-constrained devices. Summary of the Invention

[0008] To address the issue of low security in existing image encryption technologies, this invention proposes a dual-encryption image protection method based on chaotic mapping and linear congruence. By introducing chaotic sequences, the randomness and unpredictability of the key are improved, thereby significantly enhancing the security and anti-interference capabilities of image encryption.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A dual-encryption image protection method based on chaotic mapping and linear congruence method specifically includes the following steps:

[0011] S1: Obtain the image to be encrypted and convert the image into a data sequence;

[0012] S2: Obtain the first sequence to be encrypted by scrambling the data sequence using the AES encryption algorithm;

[0013] S3: Construct a chaotic system to generate a chaotic sequence, and then map and encrypt the chaotic sequence to obtain a key sequence;

[0014] S4: Perform an XOR operation on the first sequence to be encrypted and the key sequence, and output the encrypted sequence.

[0015] Preferably, S1 includes:

[0016] S1-1: Decompose the image to be encrypted into d matrices, each matrix having a size of w*h; where w represents the length of the image, h represents the width of the image, and d represents the number of channels in the image;

[0017] S1-2: Convert each matrix into a corresponding column vector by row, and then concatenate the column vectors to form a data sequence.

[0018] Preferably, S2 includes:

[0019] S2-1: Calculate the corresponding inverse element based on the AES encryption algorithm on the data sequence;

[0020] S2-2: Perform an affine transformation on the obtained inverse element to obtain the transformation parameters;

[0021] S2-3: The transformation parameters are used as new output bytes to form the entries in the S-box, i.e., the first sequence to be encrypted.

[0022] Preferably, in step S2-1, the zero element of the data sequence is mapped to a fixed value 0x63.

[0023] Preferably, in S2-2, the formula for the affine transformation is:

[0024] w=A·θ+b(1)

[0025] In formula (1), w represents the transformation parameter; A is a fixed 8×8 linear transformation matrix; b is a constant vector; and θ represents the inverse element.

[0026] Preferably, S3 includes:

[0027] S3-1: Constructing a chaotic system;

[0028] S3-2: Generate chaotic sequences based on the constructed chaotic system;

[0029] S3-3: Map the chaotic sequence to a preset interval to obtain a mapped sequence;

[0030] S3-4: Quantize the mapping sequence into 16 bits to obtain the key sequence G.

[0031] Preferably, in S3-1, the chaotic system is:

[0032]

[0033] In formula (2), x, y, and z represent the state variables of the chaotic system.

[0034] Preferably, S3-2 includes:

[0035] S3-2-1: Pre-iterate the chaotic system N1 times;

[0036] S3-2-2: Iterate the chaotic system N2 times to generate a new set of state values ​​A = A x A y A z , where A x =x1,x2,...,x k A y =y1,y2,...,y k A z =z1,z2,...,z k 0 <k≤P;x k y k z k Let P represent the state values ​​of each variable in the k-th iteration of the chaotic system, and let P represent the length of the sequence to be encrypted divided by 3.

[0037] S3-2-3: Based on the positive and negative changes in the products between the variables of state variable A, adjust the order of the state variables to generate a chaotic sequence C = C1, C2, ..., C k C k This represents the chaotic result of the k-th iteration of the chaotic system.

[0038] Preferably, in step S3-3, the input values ​​of the chaotic sequence are mapped to a preset interval [0,1] using the linear congruence method to obtain a mapped sequence:

[0039] q=a·ε+Tmodm(3)

[0040] In formula (3), q represents the value of the mapped sequence; a represents the multiplier; T represents the increment; modm represents the modulus; and ε represents the input value of the chaotic sequence.

[0041] Preferably, in step S4, the encryption sequence is calculated as follows:

[0042] First, perform an XOR operation between the first encryption sequence I and the high 8 bits and low 8 bits of the key sequence G to obtain the first calculation result and the second calculation result:

[0043] I n =i1,i2,...,i f / 2 G n =g1,g2,...,g f / 2 (4)

[0044] In formula (4), I n Indicates the first calculation result; i f / 2 Indicates the first encrypted sequence I n binary bits; G n Indicates the second calculation result; g f / 2 Represents the key sequence G in binary bits;

[0045] Then, the first calculation result is encrypted using an XOR operation to obtain an encrypted result, and multiple encrypted results are concatenated to obtain an encrypted sequence:

[0046]

[0047] In formula (5), E n G represents the encryption result. kH G represents the high f / 2 bit subsequence of the chaotic key sequence G; kL The lower f / 2 subsequence of the chaotic key sequence G is shown; This represents the XOR operation.

[0048] In summary, by adopting the above technical solution, the present invention has at least the following beneficial effects compared with the prior art:

[0049] This invention combines chaotic systems and linear congruential methods to achieve higher security and anti-interference capabilities through double encryption.

[0050] Chaotic systems, with their high degree of randomness and unpredictability, provide additional security for key generation.

[0051] Based on the design of a three-dimensional improved Lorenz chaotic system, the calculated Lyapunov exponent shows that it has significant chaotic properties, thereby enhancing the randomness and complexity of the encryption algorithm;

[0052] It employs simple and easy-to-implement algorithms (such as XOR operation) to avoid complex calculations and anti-saturation processing, while ensuring consistency in the encryption and decryption process;

[0053] It provides efficient encryption while significantly reducing hardware requirements, making it suitable for a wide range of application scenarios;

[0054] The sensitivity of chaotic sequences to initial conditions provides an additional layer of security for image encryption, effectively resisting various attack methods such as differential attacks and statistical feature attacks, thus improving security.

[0055] It has strong resistance to random interference and noise, and is particularly suitable for scenarios with high reliability requirements such as military communications and security monitoring.

[0056] The chaotic system in the design has good scalability, can adapt to different encryption requirements, and supports multi-dimensional and multi-scenario applications;

[0057] This method is entirely software-based, requiring no additional hardware costs, thus improving its cost-effectiveness in practical applications. Attached image description:

[0058] Figure 1 This is a schematic diagram of a dual-encryption image protection method based on chaotic mapping and linear congruence method according to an exemplary embodiment of the present invention.

[0059] Figure 2 This is a schematic diagram illustrating the process of decomposing a three-channel image to be encrypted into a data sequence according to an exemplary embodiment of the present invention. Detailed Implementation

[0060] The present invention will be further described in detail below with reference to embodiments and specific implementation methods. However, this should not be construed as limiting the scope of the above-described subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0061] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0062] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0063] like Figure 1 As shown, this invention provides a dual-encryption image protection method based on chaotic mapping and linear congruence method, specifically including the following steps:

[0064] S1: Obtain the image to be encrypted and convert the image into a data sequence.

[0065] like Figure 2 As shown, it specifically includes:

[0066] S1-1: Decompose the image to be encrypted (e.g., a three-channel RGB image) into d matrices, with a size of w*h; where w represents the length of the image, h represents the width of the image, and d represents the number of channels of the image.

[0067] S1-2: Convert each matrix into a corresponding column vector by row, and then concatenate the column vectors in sequence (e.g., connect the first and second columns together) to form a complete data sequence.

[0068] S2: Based on the AES encryption algorithm, the data sequence is scrambled to obtain the first sequence to be encrypted.

[0069] S2-1: Finite field GF(2) based on AES encryption algorithm 8 The data sequence is calculated to obtain the corresponding inverse element.

[0070] For each input byte (referring to the data sequence output by S1), first find its value in the finite field GF(2). 8 The inverse element in the S-box is used to construct the S-box. The inverse element is the element that, for a given element x, has an inverse element x. -1 This makes their product equal to 1, i.e., x·x -1 =1.

[0071] In this embodiment, the S-box (Substitution Box) is an important component of the AES algorithm. It increases the complexity of the cipher by applying a non-linear substitution operation to each data block (byte), making the encryption more difficult to crack through simple linear analysis.

[0072] The AES encryption process involves several steps, one of which is scrambling using an S-box. In the AES algorithm, the S-box performs byte substitution during encryption, replacing each input byte (a number between 0 and 255) with a new byte to form a new data block.

[0073] 1. Structure of the S-box

[0074] AES uses a fixed S-box for byte substitution operations. This S-box is a non-linear substitution table that maps each byte (8 bits, 0–255). The design of the S-box is based on mathematically irreversible functions; specifically, it uses the inverse element operation over GF(2^8) (a finite field) and an affine transformation.

[0075] The construction process of the S-box includes the following steps:

[0076] Inverse: First, the input value of the AESS-box is considered as an element over GF(2^8), and the inverse of that element is calculated first (in a finite field).

[0077] Affine transformation: Then, the inverse element is transformed by an affine transformation (a linear transformation plus a constant) to obtain the final S-box output.

[0078] 2. Construction process of S-box

[0079] Suppose we want to encrypt a byte x (with a value ranging from 0 to 255). First:

[0080] Consider x as an element in the finite field GF(2^8).

[0081] By performing the inverse operation on x, we obtain its inverse element in GF(2^8).

[0082] Perform an affine transformation on the obtained inverse element, and obtain the output of the S-box using a predefined matrix and constants.

[0083] The design of the S-box creates a strong non-linear relationship between its output and input, which ensures the security of AES.

[0084] 3. S-box scrambling in AES

[0085] In the AES encryption process, S-box scrambling occurs during the SubBytes step. This step performs the following operations on each byte:

[0086] SubBytes: For each byte x, find the corresponding value S(x) in the S-box and replace the original byte with the value at the corresponding position in the S-box. The purpose of this step is to break the linear structure of the input bytes, making the ciphertext more random.

[0087] For example, if the input block contains the byte 0x32, it might be replaced with 0x87 after an S-box lookup. This byte substitution is irreversible, thus increasing the strength of the cipher.

[0088] 4. Application of S-box in AES encryption process

[0089] In AES encryption, S-box scrambling is achieved through multiple rounds of SubBytes steps. In each round, the input data (data block) is broken down into multiple bytes, and each byte is replaced using an S-box. The specific process is as follows:

[0090] AddRoundKey: Performs an XOR operation between the input data and the round key.

[0091] SubBytes: Apply S-box substitution (scrambling) to each byte.

[0092] ShiftRows: Shifts data rows cyclically.

[0093] MixColumns (only in all rounds except the last one): Performs matrix transformations on data columns to increase the data's versatility.

[0094] AddRoundKey: Performs an XOR operation with the round key again.

[0095] These steps will be repeated multiple times until the encrypted ciphertext is finally obtained.

[0096] In this embodiment, the core design principle of the S-box is to enhance the non-linearity of encryption. In the AES algorithm, the role of S-box scrambling is as follows:

[0097] Increasing cryptographic complexity: By replacing one byte of input with another, the S-box scrambles the structure of the data, making the relationship between the output and input highly complex. Without a suitable key, the output value cannot be predicted.

[0098] Enhanced resistance to attacks: The nonlinear properties of S-boxes are crucial for resisting linear attacks, differential attacks, and other mathematical attacks.

[0099] Increased encryption strength: The S-box provides irreversible transformations, making it difficult to reverse-engineer the original data or key even if some bytes in the encryption process are analyzed.

[0100] AES's S-box design prioritizes security, employing numerous mathematical techniques to ensure robust resistance to attacks. The S-box design enhances security in the following ways:

[0101] Unpredictability: The S-box is carefully designed to ensure that the output of each byte substitution operation is unpredictable, reducing direct inference from the original data.

[0102] Resistance to differential attacks: A differential attack is an attack method that cracks the key by analyzing the differences between the input and output during the encryption process. The AES S-box is designed to avoid patterns that are easily exploited by differential attacks, thus improving its resistance to such attacks.

[0103] Resistance to linear attacks: Linear attacks rely on finding a linear relationship between the input and output. AES's S-box makes such attacks very difficult through its highly nonlinear substitution behavior.

[0104] In this embodiment, calculating the inverse element of the input byte requires the use of the finite field GF(2). 8 The multiplication rule is achieved by solving a specific polynomial (this is existing technology, so it will not be elaborated here).

[0105] In this embodiment, within the finite field GF(2) 8 In S-box construction, the zero element 0x00 has no inverse element. Therefore, the zero element is specially handled during the construction of the S-box and is usually mapped to a fixed value of 0x63 to avoid errors.

[0106] S2-2: Perform an affine transformation on the obtained inverse element to obtain the transformation parameters.

[0107] In this embodiment, a fixed linear affine transformation is used to further scramble the structure of the inverse element. The formula for the affine transformation is:

[0108] w=A·θ+b(1)

[0109] In formula (1), w represents the transformation parameter; A is a fixed 8×8 linear transformation matrix; b is a constant vector; and θ represents the inverse element. The purpose of affine transformation is to enhance the unpredictability and resistance to linear attacks of the S-box, making the output of the S-box difficult to derive from simple linear relationships.

[0110] S2-3: The transformation parameters are used as new output bytes to form entries in the S-box.

[0111] In this embodiment, after the above steps (S2-1, S2-2, S2-3), a corresponding output byte is generated for each input byte (0 to 255). The entire S-box is a lookup table of size 256, containing the mapping from input bytes to output bytes. This achieves the scrambling operation of the image sequence, which is also the initial encryption of the image sequence, resulting in the first encrypted sequence I.

[0112] S3: Construct a chaotic system to generate a chaotic sequence, and then map and encrypt the chaotic sequence to obtain a key sequence.

[0113] S3-1: Constructing a chaotic system.

[0114] Chaos is a deterministic, quasi-random process that occurs in nonlinear dynamic systems. This process is neither periodic nor convergent, and it is sensitive to initial values. Its behavior is characterized by uncertainty, non-repeatability, and unpredictability.

[0115] This invention constructs a new three-dimensional chaotic system based on the three-dimensional improved Lorenz chaotic system:

[0116]

[0117] In formula (2), x, y, and z represent the state variables of the chaotic system. The Lyapunov exponents can be used to determine whether the system has chaotic characteristics. The Lyapunov exponents are an important indicator for quantifying the sensitivity of a system to initial conditions. A positive Lyapunov exponent indicates that the system has an exponential sensitivity to small changes in initial conditions. This behavior is a typical characteristic of chaotic systems.

[0118] For constructing a chaotic system, numerical analysis yielded a Lyapunov exponent of 3.2221,0,-21.2458, indicating that the constructed chaotic system possesses chaotic characteristics. This invention uses this novel chaotic system as a basis to generate chaotic sequences.

[0119] S3-2: Generate chaotic sequences based on the constructed chaotic system.

[0120] Due to the high randomness and complexity of chaotic systems, specific quantization algorithms transform chaotic sequences into the desired form, enhancing the security of encryption algorithms. The specific operation is as follows:

[0121] S3-2-1: Iterate the chaotic system N1 times to eliminate the transient effects of the chaotic system entering a chaotic state.

[0122] S3-2-2: Iterate the chaotic system N2 times to generate a new set of state values ​​A = A x A y A z , where A x =x1,x2,...,x k A y =y1,y2,...,y k A z =z1,z2,...,z k 0 <k≤P;x k y k z k Let P represent the state values ​​of each variable in the k-th iteration of the chaotic system, and let P represent the length of the sequence to be encrypted divided by 3.

[0123] S3-2-3: Based on the positive and negative changes in the product between the variables of state variable A (e.g., x...) k vy k x k ·z k z k ·y k Adjust the order of the state variables to generate a chaotic sequence C = C1, C2, ..., C k C k This represents the chaotic result of the k-th iteration of the chaotic system. The mapping relationship between the sorting rules of the chaotic sequence C and the state variable A is shown in Table 1.

[0124] Table 1. Mapping relationship between the sorting rules of the chaotic sequence C and the state variable A.

[0125]

[0126] S3-3: Map the chaotic sequence to a preset interval to obtain a mapped sequence.

[0127] Since the chaotic sequence generated by S3-2 has a large value range, it cannot be effectively controlled within the range of [0,1], which will adversely affect the next step of chaotic encryption (in XOR operation, the input value range is best between [0,1], so as to avoid the scaling problem of the input value detection). Therefore, mapping the input value of the chaotic sequence to the preset interval [0,1] by using the linear congruential method can further improve the nonlinearity of the chaotic sequence.

[0128] In this embodiment, the objective function of the linear congruential method is as follows:

[0129] q=a·ε+Tmodm(3)

[0130] In formula (3), the values ​​of a, T, and modm directly affect the quality, periodicity, and efficiency of the generated mapping sequence. modm represents the modulus, which is usually a large prime number to ensure a long period, with a common value of 2^32. The value of the multiplier a ensures that the generated sequence has good periodicity and uniformity, with a common value of 1664525. The increment T also affects the quality of the generated sequence, and a non-zero value is usually chosen that is coprime with the modulus m to avoid generating repeated sequences, with a common value of 1. ε represents the input value of the chaotic sequence, and q represents the value of the mapping sequence.

[0131] S3-4: Quantize the mapping sequence into 16 bits to obtain the key sequence G.

[0132] S4: To demonstrate the simplicity and nonlinear advantages of chaotic key implementation, and to fully leverage the advantages of ciphertext interleaving and diffusion technology in image encryption, thereby enhancing its resistance to illegal attacks, this invention employs the XOR operation method for image encryption. Its characteristics include applicability to image signal encryption, nonlinear ciphertext, ease of implementation, and improved ciphertext diffusion speed.

[0133] XORing the first encryption sequence I with the high 8 bits and low 8 bits of the key sequence G respectively yields the first calculation result and the second calculation result:

[0134] I n =i1,i2,...,i f / 2 G n =g1,g2,...,g f / 2 (4)

[0135] In formula (4), I n Indicates the first calculation result; i f / 2 Indicates the first encrypted sequence I n binary bits; G n Indicates the second calculation result; g f / 2 The key sequence G represents binary bits; f = 16.

[0136] For example, I n If it is 8 bits, it is represented as i1, i2, ..., i8, where i1, i2, ..., i8 can take the values ​​0 or 1, because the operation of equation (5) is a bitwise XOR operation, which is used here for the convenience of description.

[0137] Then, the first calculation result is encrypted using an XOR operation to obtain the encrypted result. Finally, multiple encrypted results are concatenated (e.g., first and last characters are linked together) to obtain the encrypted sequence.

[0138]

[0139] In formula (5), E n G represents the encryption result. kH G represents the high f / 2 bit subsequence of the chaotic key sequence G; kL The lower f / 2 subsequence of the chaotic key sequence G is shown; This represents the XOR operation.

[0140] In the field of protecting the privacy of critical robot data, the chaotic image encryption method of this invention can ensure that sensitive data generated by robots when performing tasks, such as operation instructions and sensor information, are highly encrypted during storage or transmission. Even if the data is intercepted, it cannot be decrypted, effectively preventing data leakage and unauthorized access, and protecting the privacy of enterprises and individuals.

[0141] In military communications, the secure transmission of image data is crucial. The chaotic image encryption method of this invention can be applied to UAV image reconnaissance transmission systems. Image information collected by the UAV is encrypted using this method before transmission. Even if the data is intercepted during transmission, it cannot be decrypted due to the high level of encryption protection, thus ensuring the security of sensitive information.

[0142] In the field of security monitoring, surveillance images often contain personal privacy or sensitive information. By using the technology of this invention, surveillance images undergo high-level encryption before storage or transmission, effectively preventing data leakage even if the surveillance data is illegally accessed.

[0143] For image data involving personal privacy, such as medical images, the encryption technology of this invention can be used to protect patient information from unauthorized access. Even if the encrypted image data is stolen during cloud storage or transmission, it cannot be illegally deciphered, thus ensuring the security of personal information.

[0144] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes can be made in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A double encryption image protection method based on chaotic mapping and linear congruential method, characterized by, Specifically comprising the following steps: S1: obtaining an image to be encrypted, and converting the image into a data sequence; S2: performing image sequence permutation on the data sequence based on an AES encryption algorithm to obtain a first to-be-encrypted sequence; S3: constructing a chaotic system to generate a chaotic sequence, and performing mapping encryption on the chaotic sequence to obtain a key sequence; S4: performing exclusive OR operation on the first to-be-encrypted sequence and the key sequence to output an encrypted sequence; The S2 comprises: S2-1: calculating the data sequence based on the AES encryption algorithm to obtain a corresponding inverse element; S2-2: performing affine transformation on the obtained inverse element to obtain a transformation parameter; The formula of the affine transformation is: In equation (1), denotes the transformation parameters; is a fixed linear transformation matrix; is a constant vector; denotes the inverse element; S2-3: taking the transformation parameter as a new output byte to form an entry in an S-box, that is, the first to-be-encrypted sequence; The S3 comprises: S3-1: constructing a chaotic system; S3-2: generating a chaotic sequence based on the constructed chaotic system; S3-3: mapping the chaotic sequence to a preset interval to obtain a mapping sequence; S3-4: performing 16-bit quantization on the mapping sequence to obtain a key sequence G; In the S3-1, the chaotic system is: （2） In formula (2), x, y, and z represent state variables of the chaotic system.

2. The double encryption image protection method based on chaotic mapping and linear congruential method as claimed in claim 1, wherein, The S1 comprises: S1-1: decomposing the image to be encrypted into d matrices, and the size of the matrix is w*h; wherein w represents the length of the image, h represents the width of the image, and d represents the channel number of the image; S1-2: converting each matrix into a corresponding column vector according to rows, and then sequentially connecting the column vectors to form a data sequence.

3. The double encryption image protection method based on chaotic mapping and linear congruential method as claimed in claim 1, wherein, In S2-1, the zero elements of the data sequence are mapped to a fixed value .

4. The double encryption image protection method based on chaotic mapping and linear congruential method as claimed in claim 1, wherein, The S3-2 comprises: S3-2-1 : Pre-iteration of chaotic system seconds; S3-2-2: iterate the chaotic system again a new set of state values wherein, , , , ; , , denote the state values of the variables of the chaotic system at the kth iteration, denotes the length of the sequence to be encrypted divided by 3; S3-2-3: According to the positive and negative changes of the product of each variable of the state variable A, adjust the order of the state variable to generate a chaotic sequence ; represents the chaotic result of the kth iteration of the chaotic system.

5. The double encryption image protection method based on chaotic mapping and linear congruential method as claimed in claim 1, wherein, In the S3-3, the input value of the chaotic sequence is mapped to a preset interval [0, 1] through a linear congruential method to obtain a mapping sequence: In Equation (3), q represents a mapped sequence value; a represents a multiplier; and T represents an increment. represents a modulus; represents an input value of the chaotic sequence.

6. The double encryption image protection method based on chaotic mapping and linear congruential method as claimed in claim 1, wherein, In the S4, the calculation of the encrypted sequence is: First, performing exclusive OR operation on the high 8 bits and the low 8 bits of the first encrypted sequence I and the key sequence G respectively to obtain a first calculation result and a second calculation result: ， In formula (4), This indicates the first calculation result; Indicates the first encrypted sequence binary bits; This indicates the second calculation result; Represents the key sequence G in binary bits; Then, performing image encryption on the first calculation result based on the exclusive OR operation to obtain an encrypted result, and splicing multiple encrypted results to obtain an encrypted sequence: In Equation (5), represents an encryption result, represents a high f / 2-bit sub-sequence of the chaotic key sequence G; represents a low f / 2-bit sub-sequence of the chaotic key sequence G; represents an XOR operation.

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