Multi-medical image encryption method based on three-dimensional hyperchaotic system

Abstract

The invention relates to a multi-medical image encryption method based on a three-dimensional hyperchaotic system, and belongs to the technical field of medical image encryption. According to the method, in an image preprocessing stage, dual medical images are fused through an Alpha channel to generate a to-be-encrypted matrix, an SHA-512 function is combined with RGB and an Alpha channel matrix to generate a key sequence, and a dual-key matrix and a chaotic sequence are generated through a three-dimensional hyperchaotic Logistic-Sink (3D-HCLSM) system; in the encryption stage, triple encryption operations are implemented: a parameter randomization dynamic Josephh scrambling strategy is adopted to generate a primary ciphertext, an improved zigzag bidirectional cross permutation strategy is adopted, pixel diffusion with a key matrix is carried out to obtain a secondary ciphertext, a novel bit-level scrambling strategy is carried out, and bit XOR operation with the key matrix is carried out to complete final encryption. According to the method, a dynamic Joseph traversal mechanism with random parameters is provided, an optimized zigzag replacement strategy and a novel bit-level processing technology are combined, and the attack resistance and safety of medical image encryption are remarkably improved through the synergistic effect of multi-level chaos secret keys.

Description

Technical Field

[0001] The present invention relates to a multi-medical image encryption method based on a three-dimensional hyperchaotic system, which belongs to the technical field of medical image encryption and is suitable for synchronous secure transmission and storage of multi-source medical images such as CT (computed tomography), MRI (magnetic resonance imaging), and PET (positron emission tomography). Background Art

[0002] The large-scale deployment of medical information systems and the normalized operation of telemedicine have accelerated the digitalization of the medical imaging data chain (transmission-storage-call). However, the multi-link data interaction and cloud hosting model significantly amplify the potential risks of privacy leakage and unauthorized access. Therefore, ensuring the security and privacy of medical image data is crucial to safeguarding the rights and interests of patients, complying with laws and regulations, and enhancing the credibility of medical institutions.

[0003] In this context, it is particularly urgent to develop a reliable and efficient medical image encryption technology. Existing medical image encryption methods usually only support the encryption of a single image, while methods that can process multiple images are often inefficient and difficult to meet the needs of practical applications. Therefore, there is an urgent need for a technology that can support the encryption of multiple medical images while ensuring high efficiency. This technology must not only be able to resist various potential security threats, but also be able to achieve rapid encryption and decryption of medical images without sacrificing image quality, thereby effectively ensuring the security of medical images during transmission and storage, and ensuring that patient privacy is fully protected.

[0004] In recent years, chaotic systems have received extensive attention in the field of image encryption due to their complex dynamic behavior and high randomness. The sequences generated by chaotic systems are unpredictable and sensitive to initial values, which can provide a strong random foundation for encryption algorithms. Based on chaos theory and the above-mentioned needs, this paper proposes a multi-medical image encryption method based on a three-dimensional hyperchaotic system, aiming to improve the security and privacy of medical images through innovative encryption technology. Summary of the invention

[0005] The purpose of the present invention is to provide a multi-medical image encryption method based on a three-dimensional hyperchaotic system, aiming to solve the technical problem that existing medical image encryption methods are difficult to support encryption of multiple medical images while ensuring high efficiency.

[0006] To achieve the above object, the technical solution of the present invention is as follows: a multi-medical image encryption method based on a three-dimensional hyperchaotic system, specifically comprising the following steps:

[0007] Step 1: Perform dual image fusion preprocessing to synthesize the two original medical images into a four-channel matrix to be encrypted through the Alpha channel;

[0008] Step 2: Construct a chaotic key system. Based on the preprocessed fusion image data, extract the four-channel matrix to be encrypted as the input of the hash function, and combine the obtained results with the chaotic sequence generated by the 3D-HCLSM system to construct the key sequence;

[0009] Step 3: Perform iterative operation of the chaotic system, input two sets of preset initial parameters and the constructed key sequence into the 3D-HCLSM system, iteratively generate two key matrices key_matrix1 and key_matrix2, and an auxiliary chaotic sequence chaos_sequence;

[0010] Step 4: Perform pixel-level dynamic scrambling, use the parameter randomized dynamic Joseph scrambling strategy to perform L rounds of scrambling on the fused image to generate a primary ciphertext image;

[0011] Step 5: Implement spatial-numerical joint encryption on the primary ciphertext image, reconstruct the pixel distribution through the improved zigzag bidirectional cross-permutation strategy, and perform nonlinear diffusion calculation based on the key matrix key_matrix1 to generate a secondary ciphertext image;

[0012] Step 6: Complete the bit-level ultimate encryption, generate the Joseph scrambling rules through the parameter randomized dynamic Joseph scrambling strategy, and the chaotic sequence scrambling rules generated based on the auxiliary chaotic sequence chaos_sequence, perform a new bit-level decomposition scrambling operation on the secondary ciphertext image, reorganize it, and then perform a bitwise XOR operation with the key matrix key_matrix2 to generate the final encrypted image.

[0013] The step 1 is specifically as follows:

[0014] Step 1.1: Normalize the size of the original medical images image1 and image2, convert them into RGBA four-channel mode, and generate standardized image data containing RGB three channels and Alpha transparent channel;

[0015] Step 1.2: Perform weighted blending calculation on the RGB channels of the two original medical images and retain the transparency information of the Alpha channel to ensure the reversibility and integrity of the blended data;

[0016] Step 1.3: Reconstruct the fused RGB channel and Alpha channel into multi-dimensional data to form a structured image array, convert its data format, and output a data set before encryption that includes the fused image, RGB channel matrix, and Alpha channel matrix.

[0017] The step 2 is specifically as follows:

[0018] Step 2.1: Take the RGB channel matrix and Alpha channel matrix to be encrypted as input, use the hash function to generate a 512-bit binary hash value, and then convert it into decimal in groups of 8 bits to obtain a hash sequence of length 64, recorded as: ;

[0019] Step 2.2: Set the preset system variables and control parameters Save as initial key, and save the initial key Bring it into the 3D-HCLSM system for iteration. The number of iterations is three times the size of the image pixel. Three chaotic sequences are obtained, which are recorded as ,in Indicates the size of the image;

[0020] Step 2.3: Select the chaotic sequence , and then operate it with the hash sequence to get the key sequence , the specific calculation formula is:

[0021]

[0022] in, Indicates an XOR operation. represents the modulus operation, This is to prevent the value from overflowing the range of 0 to 255.

[0023] The step 3 is specifically as follows:

[0024] Step 3.1: Set the preset initial value The generated key sequences are input into the 3D-HCLSM system in sequence and iterated respectively. The number of iterations is three times the number of pixels. Three chaotic sequences are generated in each iteration, and two groups of chaotic sequences are generated, which are recorded as Chaotic_sequences1 and Chaotic_sequences2 respectively.

[0025] Step 3.2: respectively intercept the second half of the three chaotic sequences in Chaotic_sequences1 and Chaotic_sequences2, and splice them into a sequence of image size, and construct two key matrices key_matrix1 and key_matrix2 after rounding up;

[0026] Step 3.3: The resulting chaotic sequence The second half of is concatenated into a one-dimensional chaotic sequence chaos_sequence of the total number of image pixels, which is used to construct chaotic sequence scrambling rules.

[0027] The step 4 is specifically as follows:

[0028] Step 4.1: Flatten the obtained fused image into a one-dimensional array, recorded as mixed_image_array, and create an index array of the same size;

[0029] Step 4.2: According to the chaotic sequence generated by the 3D-HCLSM system, randomly determine the starting position start and the interval step from the key sequence keys;

[0030] Step 4.3: According to the total number of pixels, the determined starting position and the interval, the index array is used to perform a parameter randomization dynamic Joseph scrambling operation to generate a permuted index list;

[0031] Step 4.4: According to the permuted index list, rearrange the flattened pixel array mixed_image_array to obtain a scrambled pixel array;

[0032] Step 4.5: Resize the scrambled pixel array to the same size as the fused image to generate a scrambled image;

[0033] Step 4.6: Replace the fused image with the generated scrambled image, repeat steps 4.1 to 4.5 for a preset number of rounds L, and obtain the primary ciphertext image.

[0034] The step 5 is specifically as follows:

[0035] Step 5.1: Divide the obtained primary ciphertext image into several pixel blocks, each block size is ;

[0036] Step 5.2: Divide the pixels into blocks and perform an improved zigzag bidirectional cross scrambling operation to obtain the scrambling matrix corresponding to each block;

[0037] Step 5.3: If all pixel blocks are scrambled, proceed to step 5.4; otherwise, proceed to step 5.2.

[0038] Step 5.4: Merge the scrambled matrices of all pixel blocks to form an intermediate image;

[0039] Step 5.5: Perform nonlinear diffusion calculation on the intermediate image and the key matrix key_matrix1 to generate a secondary ciphertext image.

[0040] The step 5.2 is specifically as follows:

[0041] Step 5.2.1: Select two different center points in the pixel block and define a diffusion direction for each center point, and the two directions do not overlap;

[0042] Step 5.2.2: Generate two independent subsequences along the two directions respectively: the first subsequence starts from the first center point and diffuses along the first direction; the second subsequence starts from the second center point and diffuses along the second direction; each subsequence contains pixel values ​​selected from the respective center point and along the respective direction;

[0043] Step 5.2.3: Cross-merge the two subsequences generated in 5.2.2 to obtain the long sequence of the pixel block;

[0044] Step 5.2.4: Adjust the long sequence to a matrix with the same size as the pixel block before scrambling to obtain the scrambled matrix of the pixel block.

[0045] The step 6 is specifically as follows:

[0046] Step 6.1: Divide the obtained secondary ciphertext image into several D Pixel blocks of size F;

[0047] Step 6.2: Convert each pixel block into a binary matrix, decompose it into 8 bit planes based on the bit plane decomposition principle, implement a novel bit-level scrambling operation, and generate a scrambled pixel block;

[0048] Step 6.3: After all pixel blocks are scrambled, all scrambled pixel blocks are concatenated into a pixel matrix of the same size as the secondary ciphertext image, and a bitwise XOR operation is performed with the key matrix key_matrix2 to generate the final encrypted image.

[0049] The step 6.2 is specifically as follows:

[0050] Step 6.2.1: Let the 8 bit planes of each pixel block be ;

[0051] Step 6.2.2: Group the 8 bit planes. The first group of planes is , the second set of planes is ;

[0052] Step 6.2.3: Spread the generated chaotic sequence chaos_sequence to include All the numbers in generate the chaotic sequence scrambling rules. The specific generation formula is as follows:

[0053]

[0054] In the formula, is the scrambling rule of the generated chaotic sequence, Represents the chaotic sequence chaos_sequence, yes Middle Chaotic sequence value, is the size of the pixel block, and Respectively The maximum and minimum values ​​of Indicates rounding operation;

[0055] Step 6.2.4: Apply the parameter randomized dynamic Joseph scrambling strategy to the first set of planes to obtain the scrambled planes ; The second set of planes uses the generated chaotic sequence scrambling rule to obtain the scrambled plane ;

[0056] Step 6.2.5: Scramble the plane Reassemble and construct each pixel value in bit order to generate a scrambled pixel block.

[0057] The 3D-HCLSM is specifically:

[0058]

[0059] in, Is a system variable The iteration value of is the control parameter, n is the modulus coefficient,

[0060] Ensure that the chaotic system is globally bounded in the phase space. The 3D-HCLSM system is developed on the basis of the existing one-dimensional logistic mapping (Logistic mapping) and sine mapping (Sine mapping). Compared with the one-dimensional chaotic mapping Logistic and Sine, the improved 3D-HCLSM system has a wider parameter space, a larger Lyapunov exponent, and a more complex dynamic behavior, which provides good randomness and security for the encryption algorithm of the present invention.

[0061] The beneficial effects of the present invention are as follows: the present invention first constructs a three-dimensional Logistic-Sine mapping, which is developed on the basis of the existing one-dimensional Logistic mapping and Sine mapping. Secondly, image preprocessing and key generation, two target medical images are synthesized into a four-channel matrix to be encrypted through the Alpha channel, and then the RGB channel and Alpha channel of the fused medical image are used as input, and the key sequence is generated in combination with the SHA-512 hash function, and the key sequence is used for the parameter randomized dynamic Joseph scrambling process, thereby significantly enhancing the randomness of the pixel scrambling. Then, the present invention improves the traditional zigzag scrambling method, allowing the center point to be randomly selected for bidirectional scrambling, and adopts an alternating merging strategy when merging sequences, further enhancing the chaos of the pixels. Finally, the present invention proposes a new bit-level scrambling technology, which combines the parameter randomized dynamic Joseph scrambling rule and the scrambling rule based on the chaotic sequence, realizes the deep chaos of the pixels, thereby greatly improving the security of encryption. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a flow chart of the multi-medical image encryption method based on three-dimensional hyperchaotic system of the present invention;

[0063] Figure 2 is the bifurcation diagram of the 3D-HCLSM system of the present invention, where Figure 2 (a) is the bifurcation diagram of the system variable xi, Figure 2 (b) is the bifurcation diagram of the system variable yi, Figure 2 (c) is the bifurcation diagram of the system variable zi;

[0064] Figure 3 is the three-dimensional phase space trajectory diagram of the 3D-HCLSM system of the present invention, wherein Figure 3 (a) is the trajectory diagram of xi, Figure 3 (b) is the yi trajectory diagram, Figure 3 (c) is the trajectory diagram of zi, Figure 3 (d) is the xi-yi-zi trajectory diagram;

[0065] Figure 4 is a Lyapunov index diagram of the three-dimensional hyperchaotic system 3D-HCLSM system of the present invention;

[0066] Figure 5 is an improved zigzag scrambling operation diagram of the present invention;

[0067] Figure 6 It is a novel bit-level scrambling operation diagram of the present invention;

[0068] Figure 7 is a flow chart of the parameter randomization dynamic Joseph scrambling phase of the present invention;

[0069] Figure 8 It is a flow chart of the improved zigzag scrambling diffusion phase of the present invention;

[0070] Fig. 9 It is a flow chart of the novel bit-level scrambling diffusion phase of the present invention;

[0071] Fig.10 is the image encryption and decryption experimental result diagram of the present invention, wherein Fig.10 (a) Fig.10 (b) is the original image, Fig.10 (c) is the image after the two original images are mixed. Fig.10 (d) is the encrypted image, Fig.10 (e) Fig.10 (f) is the decrypted image;

[0072] Fig.11 is the comparison chart of plaintext and ciphertext histogram, where Fig.11 (a) Fig.11 is (b) plaintext and plaintext histogram, Fig.11 (c) Fig.11 (d) is the ciphertext and the ciphertext histogram;

[0073] Fig.12 is the plaintext-ciphertext pixel correlation graph, where Fig.12 (a) is the original image, Fig.12 (b) is the pixel correlation of the original image, Fig.12 (c) is the secret image, Fig.12 (d) is the pixel correlation of the dense image;

[0074] Fig.13 It is the anti-noise ability test diagram, where Fig.13 (a) Fig.13 (e) is the original medical image, Fig.13 (b) Fig.13 (c) Fig.13 (d) is the decrypted image after being attacked by Gaussian noise of different intensities. Fig.13 (f) Fig.13 (g) Fig.13 (h) is the decrypted image under salt and pepper noise attacks of different intensities. DETAILED DESCRIPTION

[0075] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0076] Example 1: Figure 1 As shown in FIG. 1 , a multi-medical image encryption method based on a three-dimensional hyperchaotic system is described. The specific operations are as follows:

[0077] Image preprocessing stage:

[0078] Perform dual image fusion preprocessing, synthesize the two original medical images into a four-channel matrix to be encrypted through the Alpha channel, and generate the original image Mixed_image before encryption. Its size is recorded as .

[0079] Key generation phase:

[0080] The RGB channel matrix and Alpha channel matrix of the image Mixed_image obtained in the preprocessing stage are used as input, and the SHA-512 hash function is used to generate a 512-bit binary sequence, which is then converted into decimal in groups of 8 bits to generate a hash sequence of length 64, recorded as: ;

[0081] The initial key Bring it into the 3D-HCLSM system for iteration, the number of iterations is , which is three times the pixel size of the original image, and three chaotic sequences are obtained, denoted as ;

[0082] Select Chaotic Sequence , XOR it with the hash sequence to get the key sequence , the specific calculation formula is:

[0083]

[0084] in, Indicates an XOR operation. represents the modulus operation, This is to prevent the value from overflowing the range of 0 to 255.

[0085] Generate two key matrices for the pixel diffusion stage and a chaotic sequence for the new bit-level scrambling. The specific steps are as follows:

[0086] The preset initial value The generated key sequences are input into the 3D-HCLSM system in sequence and iterated respectively. The number of iterations is three times the number of pixels. Three chaotic sequences are generated in each iteration, and two groups of chaotic sequences are generated, which are recorded as Chaotic_sequences1 and Chaotic_sequences2 respectively.

[0087] The second half of the three chaotic sequences in Chaotic_sequences1 and Chaotic_sequences2 are respectively intercepted and spliced ​​into a sequence of image size, and two key matrices key_matrix1 and key_matrix2 are constructed after rounding up;

[0088] The resulting chaotic sequence The second half of is spliced ​​into a one-dimensional chaotic sequence chaos_sequence of the total number of image pixels, which is used to generate the chaotic sequence scrambling rules of the new bit-level scrambling stage. The specific generation formula is as follows:

[0089]

[0090] In the formula, is the scrambling rule of the generated chaotic sequence, Represents the chaotic sequence chaos_sequence, yes Middle Chaotic sequence value, is the size of the pixel block, and Respectively The maximum and minimum values ​​of Indicates rounding operation;

[0091] The 3D-HCLSM system is specifically:

[0092]

[0093] in, Is a system variable The iteration value of is the control parameter and n is the module coefficient.

[0094] like Figure 2 As shown, when , When The entire range of values ​​shows a high degree of irregularity and complexity, indicating that the system has entered a chaotic state. Figure 3 The three-dimensional phase space trajectory of the system is plotted, in which the entire trajectory covers the phase space, indicating that the chaotic system has complex dynamic behavior and a continuous parameter range.

[0095] like Figure 4 As shown in Figure 3, all Lyapunov exponent values ​​within the parameter range are positive, which further illustrates that the 3D-HCLSM system is chaotic and even a hyperchaotic system.

[0096] Through the analysis of the bifurcation diagram, phase space trajectory diagram and Lyapunov exponent of the chaotic system, the chaotic system proposed in the present invention has complex dynamic behavior and high randomness, and the generated sequence is unpredictable and sensitive to initial values, which can provide a strong random foundation for the medical image encryption algorithm.

[0097] Based on the traditional zigzag scrambling operation, the present invention proposes an improved zigzag bidirectional cross scrambling operation. The pixel block is taken as an example to illustrate. Figure 5 As shown, the specific steps are:

[0098] Select two different center points in the pixel block, define a diffusion direction for each center point, and randomly scramble along two directions. In the figure, the center points 28 and 37 are selected, and bidirectional diffusion is performed along the upper left and lower right respectively, obtaining two sequences, which are recorded as sub_sequence1 and sub_sequence2;

[0099] Cross-merge sub_sequence1 and sub_sequence2 to obtain the scrambled sequence List1 of the pixel block;

[0100] Reshape the sequence List1 back The scrambled image matrix is ​​obtained by dividing the image into blocks of size.

[0101] Based on the common bit-level scrambling operation, the present invention proposes a novel bit-level scrambling method. The pixel block is taken as an example to illustrate. Figure 6 As shown, the specific steps are:

[0102] First, the original image original_image pixel matrix is ​​converted into a corresponding binary matrix; then, according to the principle of bit plane decomposition of the image, the bits of the pixel values ​​are placed in the corresponding bit planes. They represent the 8 bit planes obtained after the image is decomposed;

[0103] The parameter randomized dynamic Joseph scrambling strategy proposed by the present invention is used to generate scrambling rule 1, and then the chaotic sequence chaos_sequence generated in the key generation stage is used to construct a sequence with a length of the pixel block size, while retaining the randomness of the chaotic sequence, to generate a chaotic sequence scrambling rule, which is recorded as scrambling rule 2;

[0104] The obtained 8 bit planes are grouped, the first group of planes is , apply the scrambling rule 1 Joseph scrambling, and get the corresponding scrambling plane The second set of planes is , apply scrambling rule 2 to scramble and get the scrambled bit plane ;

[0105] Scramble the plane Recombine and construct each pixel value in the order of bits to obtain a scrambled image;

[0106] The obtained scrambled image is XORed with the key matrix generated based on the 3D-HCLSM system, and finally a bit-level scrambled diffused image, i.e., an encrypted image, is generated.

[0107] Scrambling phase:

[0108] Based on the rules of the Joseph problem, the key sequence is randomly selected as the starting position start and the interval step, and the Mixed_image is dynamically randomized and Joseph scrambled to obtain the primary ciphertext image.

[0109] like Figure 7 As shown, the specific operations of the dynamic randomized Joseph scrambling stage are:

[0110] Flatten the fused image into a one-dimensional array and create an index array of the same size;

[0111] According to the chaotic sequence generated by the 3D-HCLSM system, the starting position start and the interval step are randomly determined from the key sequence keys;

[0112] According to the total number of pixels, the determined starting position and the interval, the index array is used to perform a parameter randomized dynamic Joseph scrambling operation to generate a permuted index list;

[0113] According to the permuted index list, the flattened pixel array is rearranged to obtain a scrambled pixel array;

[0114] Resize the scrambled pixel array to the same shape as the fused image to generate a scrambled image;

[0115] The fused image is replaced with the generated scrambled image, and the above steps are repeated for L rounds to obtain a primary ciphertext image, where L=2 in the present invention.

[0116] The first stage of chaos diffusion:

[0117] First, the primary ciphertext image is divided into several pixel blocks, each block size is ; Next, each block is subjected to improved zigzag bidirectional cross scrambling; then the obtained scrambling sequence and the key matrix key_matrix1 generated by the chaotic system are subjected to nonlinear diffusion operation to generate the image of the first stage of the scrambling diffusion order, that is, the secondary ciphertext image. The improved zigzag bidirectional cross scrambling diffusion operation process proposed by the present invention is as follows: Figure 8 shown.

[0118] The second stage of chaos spread:

[0119] First, the secondary ciphertext image is The size of the key is divided into several pixel blocks; then, each block is decomposed into 8 bit planes, corresponding to each bit of the pixel value. Then, the chaotic sequence generated in the key generation stage is used to scramble the rules , combined with the dynamic Joseph scrambling algorithm, the 8 bit planes of each block are subjected to alternating improved bit-level scrambling operations. After completing the bit-level scrambling, the bit planes are reassembled to form an intermediate image. Finally, the intermediate image is subjected to pixel-by-pixel XOR operation with the key matrix key_matrix2 generated by the chaotic system to obtain the image of the second stage of scrambling diffusion, that is, the final encrypted image. Fig. 9 The specific operation process of this stage is described as follows:

[0120] Divide the secondary encrypted image into pieces of size Several blocks, as shown in the figure , where block represents a pixel block;

[0121] Convert each pixel block into a corresponding binary matrix;

[0122] Decompose the binary matrix of each pixel block into the corresponding 8 bit planes;

[0123] The generated chaotic sequence scrambling rule and the dynamic randomized Joseph scrambling rule are introduced to perform alternate bit-level scrambling on the 8 bit planes of each pixel block to generate a scrambling matrix.

[0124] The obtained scrambled matrix is ​​subjected to a bitwise XOR operation with the key matrix key_matrix2 generated based on the 3D-HCLSM system to obtain the image of the second stage of scrambled diffusion, that is, the final encrypted image encrypted_image.

[0125] Fig.10 This is the simulation result of the image encryption and decryption experiment of the present invention, which confirms the effectiveness and feasibility of the encryption method. Fig.11 , Fig.12 , Fig.13 and Table 1, respectively analyze the plaintext and ciphertext histogram, pixel correlation, resistance to noise attacks, resistance to differential attacks, etc. The experimental results show the security of the multi-medical image encryption algorithm.

[0126] Table 1 Results of pixel change rate NPCR and unified average change intensity UACI

[0127] The specific implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A multi-medical image encryption method based on a three-dimensional hyperchaotic system, characterized in that: The specific implementation steps are as follows: Step 1: Perform dual image fusion preprocessing to synthesize the two original medical images into a four-channel matrix to be encrypted through the Alpha channel; Step 2: Construct a chaotic key system. Based on the preprocessed fusion image data, extract the four-channel matrix to be encrypted as the input of the hash function, and combine the obtained results with the chaotic sequence generated by the 3D-HCLSM system to construct the key sequence; Step 3: Perform iterative operation of the chaotic system, input two sets of preset initial parameters and the constructed key sequence into the 3D-HCLSM system, iteratively generate two key matrices key_matrix1 and key_matrix2, and an auxiliary chaotic sequence chaos_sequence; Step 4: Perform pixel-level dynamic scrambling, use the parameter randomized dynamic Joseph scrambling strategy to perform L rounds of scrambling on the fused image to generate a primary ciphertext image; Step 5: Implement spatial-numerical joint encryption on the primary ciphertext image, reconstruct the pixel distribution through the improved zigzag bidirectional cross-permutation strategy, and perform nonlinear diffusion calculation based on the key matrix key_matrix1 to generate a secondary ciphertext image; Step 6: Complete the bit-level ultimate encryption, generate the Joseph scrambling rules through the parameter randomized dynamic Joseph scrambling strategy, and the chaotic sequence scrambling rules generated based on the auxiliary chaotic sequence chaos_sequence, perform a new bit-level decomposition scrambling operation on the secondary ciphertext image, reorganize it, and then perform a bitwise XOR operation with the key matrix key_matrix2 to generate the final encrypted image.

2. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 1 is characterized in that: The step 1 is specifically as follows: Step 1.1: Normalize the size of the original medical images image1 and image2, convert them into RGBA four-channel mode, and generate standardized image data containing RGB three channels and Alpha transparent channel; Step 1.2: Perform weighted blending calculation on the RGB channels of the two original medical images and retain the transparency information of the Alpha channel; Step 1.3: Reconstruct the fused RGB channel and Alpha channel into multi-dimensional data to form a structured image array, convert its data format, and output a data set before encryption that includes the fused image, RGB channel matrix, and Alpha channel matrix.

3. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 1 is characterized in that: The step 2 is specifically as follows: Step 2.1: Take the RGB channel matrix and Alpha channel matrix to be encrypted as input, use the hash function to generate a 512-bit binary hash value, and then convert it into decimal in groups of 8 bits to obtain a hash sequence of length 64, recorded as: ; Step 2.2: Set the preset system variables and control parameters Save as initial key, and save the initial key Bring it into the 3D-HCLSM system for iteration. The number of iterations is three times the size of the image pixel. Three chaotic sequences are obtained, which are recorded as ,in Indicates the size of the image; Step 2.3: Select the chaotic sequence , and then operate it with the hash sequence to get the key sequence , the specific calculation formula is: ； in, Indicates an XOR operation. represents the modulus operation, This is to prevent the value from overflowing the range of 0 to 255.

4. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 1, characterized in that: The step 3 is specifically as follows: Step 3.1: Set the preset initial value The generated key sequences are input into the 3D-HCLSM system in sequence and iterated respectively. The number of iterations is three times the number of pixels. Three chaotic sequences are generated in each iteration, and two groups of chaotic sequences are generated, which are recorded as Chaotic_sequences1 and Chaotic_sequences2 respectively. Step 3.2: respectively intercept the second half of the three chaotic sequences in Chaotic_sequences1 and Chaotic_sequences2, and splice them into a sequence of image size, and construct two key matrices key_matrix1 and key_matrix2 after rounding up; Step 3.3: The resulting chaotic sequence The second half of is concatenated into a one-dimensional chaotic sequence chaos_sequence of the total number of image pixels, which is used to construct chaotic sequence scrambling rules.

5. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 1, characterized in that: The step 4 is specifically as follows: Step 4.1: Flatten the obtained fused image into a one-dimensional array, recorded as mixed_image_array, and create an index array of the same size; Step 4.2: According to the chaotic sequence generated by the 3D-HCLSM system, randomly determine the starting position start and the interval step from the key sequence keys; Step 4.3: According to the total number of pixels, the determined starting position and the interval, the index array is used to perform a parameter randomization dynamic Joseph scrambling operation to generate a permuted index list; Step 4.4: According to the permuted index list, rearrange the flattened pixel array mixed_image_array to obtain a scrambled pixel array; Step 4.5: Resize the scrambled pixel array to the same size as the fused image to generate a scrambled image; Step 4.6: Replace the fused image with the generated scrambled image, repeat steps 4.1 to 4.5 for a preset number of rounds L, and obtain the primary ciphertext image.

6. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 1, characterized in that: The step 5 is specifically as follows: Step 5.1: Divide the obtained primary ciphertext image into several pixel blocks, each block size is ; Step 5.2: Divide the pixels into blocks and perform an improved zigzag bidirectional cross scrambling operation to obtain the scrambling matrix corresponding to each block; Step 5.3: If all pixel blocks are scrambled, proceed to step 5.4; otherwise, proceed to step 5.

2. Step 5.4: Merge the scrambled matrices of all pixel blocks to form an intermediate image; Step 5.5: Perform nonlinear diffusion calculation on the intermediate image and the key matrix key_matrix1 to generate a secondary ciphertext image.

7. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 6 is characterized in that: The step 5.2 is specifically as follows: Step 5.2.1: Select two different center points in the pixel block and define a diffusion direction for each center point, and the two directions do not overlap; Step 5.2.2: Generate two independent subsequences along the two directions respectively: the first subsequence starts from the first center point and diffuses along the first direction; the second subsequence starts from the second center point and diffuses along the second direction; each subsequence contains pixel values ​​selected from the respective center point and along the respective direction; Step 5.2.3: Cross-merge the two subsequences generated in 5.2.2 to obtain the long sequence of the pixel block; Step 5.2.4: Adjust the long sequence to a matrix with the same size as the pixel block before scrambling to obtain the scrambled matrix of the pixel block.

8. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 1 is characterized in that: The step 6 is specifically as follows: Step 6.1: Divide the obtained secondary ciphertext image into several D Pixel blocks of size F; Step 6.2: Convert each pixel block into a binary matrix, decompose it into 8 bit planes based on the bit plane decomposition principle, implement a novel bit-level scrambling operation, and generate a scrambled pixel block; Step 6.3: After all pixel blocks are scrambled, all scrambled pixel blocks are concatenated into a pixel matrix of the same size as the secondary ciphertext image, and a bitwise XOR operation is performed with the key matrix key_matrix2 to generate the final encrypted image.

9. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 8, characterized in that: The step 6.2 is specifically as follows: Step 6.2.1: Let the 8 bit planes of each pixel block be ; Step 6.2.2: Group the 8 bit planes. The first group of planes is , the second set of planes is ; Step 6.2.3: Spread the generated chaotic sequence chaos_sequence to include All the numbers in generate the chaotic sequence scrambling rules. The specific generation formula is as follows: ； In the formula, is the scrambling rule of the generated chaotic sequence, Represents the chaotic sequence chaos_sequence, yes Middle Chaotic sequence value, is the size of the pixel block, and Respectively The maximum and minimum values ​​of Indicates rounding operation; Step 6.2.4: Apply the parameter randomized dynamic Joseph scrambling strategy to the first set of planes to obtain the scrambled planes ; The second set of planes uses the generated chaotic sequence scrambling rule to obtain the scrambled plane ; Step 6.2.5: Scramble the plane Reassemble and construct each pixel value in bit order to generate a scrambled pixel block.

10. The multi-medical image encryption method based on three-dimensional hyperchaotic system according to claim 1, characterized in that: The 3D-HCLSM is specifically: ； in, Is a system variable The iteration value of is the control parameter and n is the module coefficient.

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