Image encryption method based on sine transform chaotic system

Abstract

The invention relates to an efficient image encryption method based on a sine transform chaotic system, which belongs to the field of image encryption and comprises the following steps: S1: designing a novel two-dimensional chaotic structure according to the good nonlinear characteristics of a Sine function, using several classic one-dimensional chaotic maps as subsystems to generate a two-dimensional chaotic system, and using a chaotic sequence generated by the two-dimensional chaotic system for an encryption algorithm; S2: using a SHA-512 hash value of a plaintext image to generate an initial value and a control parameter of the chaotic system; S3: performing row scrambling and column scrambling on a plaintext image pixel matrix based on the chaotic sequence generated by the chaotic system and a Knuth-Durstenfeld shuffling algorithm; S4: performing a diffusion operation on a matrix obtained after the scrambling operation and a random matrix generated by the chaotic sequence, and then performing a self-diffusion operation on the obtained diffusion matrix to obtain a ciphertext image; S5: image decryption, and decrypting the encrypted image according to the inverse operations of diffusion and scrambling.

Description

Technical Field

[0001] The invention belongs to the field of image encryption and relates to an image encryption method based on a sine transform chaotic system. Background Art

[0002] With the widespread use of image information in the Internet era, how to ensure the secure transmission of images has become one of the hot topics of current scholars. Traditional encryption algorithms cannot adapt well to the needs of image encryption, so new encryption algorithms need to be studied to ensure the security and integrity of images during transmission. In the 1960s, American meteorologist Edward Norton Lorenz proposed the famous "butterfly effect" theory. Through mathematical simulation of the atmospheric circulation system, he found that a small change in initial conditions can lead to a very different long-term behavior of the system. This unpredictable and highly sensitive behavior is called "chaos" by him. In 1989, Matthews used the Logistic chaotic system to encrypt text data for the first time. In 1998, Fridrich first proposed an image encryption algorithm based on a chaotic system. The algorithm uses the Logistic chaotic system to generate a key to encrypt images. This secure and efficient image encryption method quickly attracted the attention of many scholars and finally became one of the important foundations for the study of chaos-based image encryption algorithms.

[0003] In the encryption system based on chaotic system, the security of the algorithm depends on the chaotic performance of the chaotic system used and the structure adopted by the encryption scheme. The chaotic system used in the image encryption system can be divided into low-dimensional chaotic system, high-dimensional chaotic system and composite chaotic system. Among them, the structure of low-dimensional chaotic system is relatively simple and easy to understand, and the hardware requirements for implementation are relatively low, so it is widely used in image encryption system. However, while this type of chaotic system is easy to use, it also has some potential security problems, such as uneven chaotic sequence, few chaotic parameters, easy to suffer from brute force calculation, small chaos range, etc. Compared with low-dimensional chaotic system, high-dimensional chaotic system shows more complex chaotic phenomenon, and generally has more control parameters, thereby increasing the key space and improving the security of the algorithm. However, in practical applications, due to the complex structure and high hardware design requirements of high-dimensional chaotic system, it cannot meet the requirements of efficient and fast use. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide an image encryption method based on a sine transform chaotic system. The method uses a two-dimensional chaotic structure based on a sine transform to generate a chaotic system, and uses a pseudo-random sequence generated by the chaotic system to provide random numbers for an image encryption algorithm. The proposed image encryption scheme has a fast running speed and strong security, and can well resist various attacks such as statistical attacks, brute force attacks, and plaintext / chosen plaintext attacks.

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

[0006] An image encryption method based on a sine transform chaotic system comprises the following steps:

[0007] S1: Sine transform chaotic system generation stage, design two-dimensional chaotic structure according to the good nonlinear characteristics of Sine function, use Logistic map and Tent map as subsystems to generate two-dimensional Logistic-Tent chaotic system (2D-LTCS), use Sine map and Gauss map as subsystems to generate two-dimensional Sine-Gauss chaotic system (2D-SGCS);

[0008] S2: The stage of generating the initial value and control parameters of the chaotic system, using the SHA-512 hash value of the plaintext image to generate the initial value and control parameters of 2D-LTCS and 2D-SGCS;

[0009] S3: Scrambling operation, using the Knuth-Durstenfeld shuffle algorithm to scramble the rows and columns of the plaintext image pixel matrix. The random numbers required by the scrambling algorithm are generated by 2D-LTCS;

[0010] S4: Diffusion operation: generate a random matrix based on the chaotic sequence generated by 2D-SGCS and perform an XOR operation with the scrambled matrix. After obtaining the diffusion matrix, randomly select a point for self-diffusion operation to obtain the ciphertext image.

[0011] S5: Image decryption, decrypt the encrypted image according to the inverse operations of diffusion and scrambling.

[0012] Further, the two-dimensional chaotic structure in step S1 is:

[0013]

[0014] Where F(θ,x i ) and G(ω,x i ) represent two one-dimensional chaotic systems, θ and ω are their control parameters, f(y i ) represents a linear function about y, f(x i ) represents a linear function about x;

[0015] When setting the Logistic map as F(θ,x i ), the Tent map is G(ω,x i ), f(y i )=y i 2 +1,f(x i )=x i 2 +5, the resulting 2D-LTCS is as follows:

[0016]

[0017]

[0018] When setting the Sine map as F(θ,x i ), Gauss map as G(ω,x i ), f(y i )=y i 2 +1,f(x i )=x i 2 +5, the resulting 2D-SGCS is as follows:

[0019]

[0020] Further, the generation of the initial value of the chaotic system described in step S2 is as follows:

[0021]

[0022] Where x0 and y0 are the initial values ​​of 2D-LTCS, x0 * and y0 * is the initial value of 2D-SGCS, s1,s2,…,s 63 ,s 64 The SHA-512 hash values ​​generated for the plaintext image, in groups of 8 bits;

[0023] The control parameter generation formula of the chaotic system is as follows:

[0024]

[0025] Further, in step S3, assuming that the size of the normal grayscale image is M×N, the scrambling operation steps are as follows:

[0026] S31: The number of iterations of 2D-LTCS is 1000+M×N. The results of the first 1000 iterations are discarded. The resulting chaotic sequences are called lt1 and lt2. The chaotic sequence lt1 is processed as follows:

[0027]

[0028] In the formula It means rounding down, LT2 is processed in the same way as LT1, and finally two chaotic sequences LT1 and LT2 are obtained;

[0029] S32: The specific steps of the Knuth-Durstenfeld shuffle algorithm are as follows:

[0030] S321: Create an array arr with an array size of n to store values ​​from 1 to n respectively;

[0031] S322: Generate a random number x from 0 to n-1;

[0032] S323: Output the value of arr subscripted with x, which is the first random number;

[0033] S324: swap the tail element of arr with the element with subscript x;

[0034] S325: Same as 2, generate a random number x from 0 to n-2;

[0035] S326: Output the value of arr subscripted with x, which is the second random number;

[0036] S327: Swap the second-to-last element of arr with the element with subscript x until m numbers are output.

[0037] S33: scrambling rows and columns, using the chaotic sequence LG1 as the row index sequence of the random number x generated in step S322, the method is as follows:

[0038] O row (i) = mod(LG1(i) × 10 12 ,M×Ni),i=0,1,…,M×N-1

[0039] The plaintext image P matrix of size M×N is expanded into a one-dimensional array by row, and the rows are scrambled using the Knuth-Durstenfeld shuffle algorithm; then the one-dimensional array after row scrambling is converted into a matrix, and the matrix is ​​expanded into a new one-dimensional array by column, and the chaotic sequence LG2 is used to generate a column index sequence according to the following formula:

[0040] O column (i) = mod(LG2(i) × 10 15 ,M×Ni),i=0,1,…,M×N-1

[0041] The Knuth-Durstenfeld shuffle algorithm is used again to shuffle the columns. The resulting one-dimensional array is converted into a matrix to obtain the scrambled image, which is denoted as P. D .

[0042] Further, in step S4, the diffusion step is as follows:

[0043] S41: The number of 2D-SGCS iterations is 1000+M×N. The results of the first 1000 iterations are discarded. The resulting chaotic sequences are called sg1 and sg2. The chaotic sequences sg1 and sg2 are processed as follows:

[0044]

[0045] S42: Generate random matrix R_P according to SG1 D And the scrambled matrix P D Perform XOR operation, R_P D The generated expression is as follows:

[0046]

[0047] R_P D1 (i) Transformed into D Matrix R_P with the same length and width D , the XOR operation is as follows:

[0048] N_P D (x,y)=P D (x,y)⊕R_P D (x,y)

[0049] S43: In N_P D Select a point V(X,Y) in the matrix for self-diffusion. The selection formula is as follows:

[0050]

[0051] Taking point V(X,Y) as the center, perform XOR operation to the left. The formula is as follows:

[0052] C_P(Xi,Y)=N_P(Xi,Y)⊕C_P(X-i+1,Y)

[0053] where i∈[1,X];

[0054] Taking point V(X,Y) as the center, perform XOR operation to the right. The formula is as follows:

[0055] C_P(x+i,Y)=N_P(X+i,Y)⊕C_P(X+i-1,Y)

[0056] where i∈[1,MX];

[0057] Taking point V(X,Y) as the center, perform XOR operation upwards. The formula is as follows:

[0058] C_P(X,Y+i)=N_P(X,Y+i)⊕C_P(X,Y+i-1)

[0059] where i∈[1,Y];

[0060] Taking point V(X,Y) as the center, perform XOR operation downwards. The formula is as follows:

[0061] C_P(X,Yi)=N_P(X,Yi)⊕C_P(X,Y-i+1)

[0062] where i∈[1,NY];

[0063] After completing the diffusion in all directions, the ciphertext image C_P is obtained.

[0064] Further, in step S5, the encrypted image is decrypted according to the inverse operation of diffusion and scrambling. Since the operation of the diffusion part is an XOR operation, the decryption is performed again according to the center point. In the scrambling step of decryption, according to the index sequence O column (i) and O row (i) Perform column and row transformations on the scrambled matrix to finally obtain the plaintext image.

[0065] The beneficial effects of the present invention are as follows: the present invention is an image encryption method based on a sine transform chaotic system. Compared with a classical chaotic system, the proposed chaotic system has the characteristics of high chaotic performance, uniform chaotic distribution, and a large range of control parameter values. The image encryption scheme has the characteristics of high operating efficiency and high security, and has excellent practicality. The present invention uses the hash value generated by the SHA-512 hash function of the original image and the chaotic parameter value and initial value to form a key, thereby improving the ability to resist known plaintext attacks and chosen plaintext attacks. The Knuth-Durstenfeld shuffling algorithm is used in the scrambling process, which reduces the time complexity and space complexity of the algorithm while ensuring the scrambling effect. In the diffusion process, a random matrix generated based on a sine transform chaotic system is used to perform an XOR operation with the scrambled matrix, and a random point in the matrix is ​​selected for a central self-diffusion operation, thereby ensuring the efficiency and security of the algorithm.

[0066] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0068] Figure 1 This is a framework diagram of the image encryption method based on the sine transform chaotic system of the present invention;

[0069] Figure 2 Lyapunov index diagrams of sine transform chaotic systems, where (a) is the Lyapunov index diagram of 2D-LTCS, (b) is the Lyapunov index diagram of 2D-SGCS, (c) is the Lyapunov index diagram of 2D-LGCS, and (d) is the Lyapunov index diagram of 2D-STCS. DETAILED DESCRIPTION

[0070] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0071] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0072] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0073] See also Figure 1-2The present invention provides an image encryption method based on a sine transform chaotic system, comprising the following steps:

[0074] Step 1: In the sine transform chaotic system generation stage, a two-dimensional chaotic structure is designed according to the good nonlinear characteristics of the Sine function. The Logistic map and Tent map are used as subsystems to generate a two-dimensional Logistic-Tent chaotic system (2D-LTCS), and the Sine map and Gauss map are used as subsystems to generate a two-dimensional Sine-Gauss chaotic system (2D-SGCS). The two-dimensional chaotic structure is specifically expressed as follows:

[0075]

[0076] Where F(θ,x i ) and G(ω,x i ) represent two one-dimensional chaotic systems, whose control parameters are θ and ω, respectively. i ) represents a linear function about y, f(x i ) represents a linear function about x.

[0077] When setting the Logistic map as F(θ,x i ), the Tent map is G(ω,x i ), f(y i )=y i 2 +1,f(x i )=x i 2 +5, the resulting 2D-LTCS is as follows:

[0078]

[0079]

[0080] The parameters are set to θ∈(0,10), ω∈(8,11.5).

[0081] When setting the Sine map as F(θ,x i ), Gauss map as G(ω,x i ), f(y i )=y i 2 +1,f(x i )=x i 2 +5, the resulting 2D-SGCS is as follows:

[0082]

[0083] Wherein, the control parameters are set as λ∈(0,16),ω∈(-1.6,2.6).

[0084] Step 2: In the stage of generating the initial value and control parameters of the chaotic system, the SHA-512 hash value of the plaintext image is used to generate the initial value and control parameters of 2D-LTCS and 2D-SGCS. The specific method is as follows:

[0085]

[0086] Where x0 and y0 are the initial values ​​of 2D-LTCS, x0 * and y0 * is the initial value of 2D-SGCS, s1,s2,…,s 63 ,s 64 The SHA-512 hash value generated for the plaintext image is 8 bits per group. The control parameter generation formula of the chaotic system is as follows:

[0087]

[0088] Step 3: Scrambling operation, using the Knuth-Durstenfeld shuffle algorithm to scramble the rows and columns of the plaintext image pixel matrix. The random numbers required by the scrambling algorithm are generated by 2D-LTCS. The specific method of the scrambling algorithm is as follows:

[0089] Step 1: The number of iterations of 2D-LTCS is 1000+M×N. The results of the first 1000 iterations are discarded, and the resulting chaotic sequences are called lt1 and lt2. The chaotic sequence lt1 is processed as follows: It means rounding down, LT2 is processed in the same way as LT1, and finally two chaotic sequences LT1 and LT2 are obtained;

[0090]

[0091] Step 2: The specific steps of the Knuth-Durstenfeld shuffle algorithm are as follows:

[0092] 1. Create an array arr of size n, storing values ​​from 1 to n respectively;

[0093] 2. Generate a random number x from 0 to n-1;

[0094] 3. Output the value of arr with the subscript x, which is the first random number;

[0095] 4. Swap the tail element of arr with the element with subscript x;

[0096] 5. Same as 2, generate a random number x from 0 to n-2;

[0097] 6. Output the value of arr with the subscript x, which is the second random number;

[0098] 7. Swap the second-to-last element of arr with the element with subscript x;

[0099] As above, until m numbers are output.

[0100] Step 3: Row and column scrambling. The chaotic sequence LG1 is used as the row index sequence of the random number x generated in step 2 of the Knuth-Durstenfeld shuffle algorithm as follows:

[0101] O row (i) = mod(LG1(i) × 10 12 ,M×Ni),i=0,1,…,M×N-1

[0102] The plaintext image P is expanded into a one-dimensional array by row, and the Knuth-Durstenfeld shuffle algorithm is used to scramble the rows. Then the one-dimensional array after scrambling the rows is converted into a matrix, which is expanded into a new one-dimensional array by column, and the chaotic sequence LG2 is used to generate a column index sequence according to the following formula:

[0103] O column (i) = mod(LG2(i) × 10 15 ,M×Ni),i=0,1,…,M×N-1

[0104] The Knuth-Durstenfeld shuffle algorithm is used again to shuffle the columns. The resulting one-dimensional array is converted into a matrix to obtain the scrambled image, which is denoted as P. D ;

[0105] Step 4: Diffusion operation: Generate a random matrix based on the chaotic sequence generated by 2D-SGCS and perform an XOR operation with the scrambled matrix. After obtaining the diffusion matrix, randomly select a point for self-diffusion operation to obtain the ciphertext image. The specific method of the diffusion algorithm is as follows:

[0106] Step 1: The number of 2D-SGCS iterations is 1000+M×N. The results of the first 1000 iterations are discarded, and the resulting chaotic sequences are called sg1 and sg2. The chaotic sequences sg1 and sg2 are processed as follows:

[0107]

[0108] Step 2: Generate a random matrix R_P based on SG1 D And the scrambled matrix P D Perform XOR operation, R_P D The generated expression is as follows:

[0109]

[0110] R_P D1 (i) Transformed into D Matrix R_P with the same length and width D , the XOR operation is as follows:

[0111] N_P D (x,y)=P D (x,y)⊕R_P D (x,y)

[0112] Step 3: In N_P D Select a point V(X,Y) in the matrix for self-diffusion. The selection formula is as follows:

[0113]

[0114] Taking point V(X,Y) as the center, perform XOR operation to the left. The formula is as follows:

[0115] C_P(Xi,Y)=N_P(Xi,Y)⊕C_P(X-i+1,Y)

[0116] where i∈[1,X].

[0117] Taking point V(X,Y) as the center, perform XOR operation to the right. The formula is as follows:

[0118] C_P(x+i,Y)=N_P(X+i,Y)⊕C_P(X+i-1,Y)

[0119] where i∈[1,MX].

[0120] Taking point V(X,Y) as the center, perform XOR operation upwards. The formula is as follows:

[0121] C_P(X,T+i)=N_P(X,Y+i)⊕C_P(X,Y+i-1)

[0122] where i∈[1,Y].

[0123] Taking point V(X,Y) as the center, perform XOR operation downwards. The formula is as follows:

[0124] C_P(X,Yi)=N_P(X,Yi)⊕C_P(X,Y-i+1)

[0125] Where i∈[1,NY]. After completing the diffusion in all directions, the ciphertext image C_P is obtained.

[0126] Step 5: Decrypt the encrypted image according to the inverse operation of diffusion and scrambling. Since the diffusion operation is an XOR operation, the decryption can be performed by performing an XOR operation again according to the center point. column (i) and O row (i) Perform column and row transformations on the scrambled matrix to finally obtain the plaintext image.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. An image encryption method based on a sine transform chaotic system, characterized in that: The following steps are involved: S1: Sine transform chaotic system generation stage, design two-dimensional chaotic structure according to the good nonlinear characteristics of Sine function, use Logistic map and Tent map as subsystems to generate two-dimensional Logistic-Tent chaotic system 2D-LTCS, use Sine map and Gauss map as subsystems to generate two-dimensional Sine-Gauss chaotic system 2D-SGCS; S2: The stage of generating the initial value and control parameters of the chaotic system, using the SHA-512 hash value of the plaintext image to generate the initial value and control parameters of 2D-LTCS and 2D-SGCS; S3: Scrambling operation, using the Knuth-Durstenfeld shuffle algorithm to scramble the rows and columns of the plaintext image pixel matrix. The random numbers required by the scrambling algorithm are generated by 2D-LTCS; S4: Diffusion operation: generate a random matrix based on the chaotic sequence generated by 2D-SGCS and perform an XOR operation with the scrambled matrix. After obtaining the diffusion matrix, randomly select a point for self-diffusion operation to obtain the ciphertext image. S5: Image decryption, decrypt the encrypted image according to the inverse operations of diffusion and scrambling.

2. The image encryption method based on sine transform chaotic system according to claim 1 is characterized in that: The two-dimensional chaotic structure in step S1 is: Where F(θ, x i ) and G(ω, x i ) represent two one-dimensional chaotic systems, θ and ω are their control parameters, f(y i ) represents a linear function about y, f(x i ) represents a linear function about x; When setting the Logistic map as F(θ, x i ), the Tent map is G(ω, x i ), f(y i )=y i 2 +1,f(x i )=x i 2 +5, the resulting 2D-LTCS is as follows: When setting the Sine map as F(θ, x i ), Gauss map as G(ω, x i ), f(y i )=y i 2 +1,f(x i )=x i 2 +5, the resulting 2D-SGCS is as follows:

3. The image encryption method based on sine transform chaotic system according to claim 1 is characterized in that: The generation of the initial value of the chaotic system described in step S2 is as follows: Where x0 and y0 are the initial values ​​of 2D-LTCS, x0 * and y0 * is the initial value of 2D-SGCS, s1, s2, …, s 63 ,s 64 The SHA-512 hash values ​​generated for the plaintext image, in groups of 8 bits; The control parameter generation formula of the chaotic system is as follows:

4. The image encryption method based on sine transform chaotic system according to claim 1 is characterized in that: In step S3, assuming that the size of the normal grayscale image is M×N, the scrambling operation steps are as follows: S31: The number of iterations of 2D-LTCS is 1000+M×N. The results of the first 1000 iterations are discarded. The resulting chaotic sequences are called lt1 and lt2. The chaotic sequence lt1 is processed as follows: In the formula It means rounding down, LT2 is processed in the same way as LT1, and finally two chaotic sequences LT1 and LT2 are obtained; S32: The specific steps of the Knuth-Durstenfeld shuffle algorithm are as follows: S321: Create an array arr with an array size of n to store values ​​from 1 to n respectively; S322: Generate a random number x from 0 to n-1; S323: Output the value of arr subscripted with x, which is the first random number; S324: swap the tail element of arr with the element with subscript x; S325: Same as 2, generate a random number x from 0 to n-2; S326: Output the value of arr subscripted with x, which is the second random number; S327: Swap the second-to-last element of arr with the element with subscript x until m numbers are output; S33: scrambling rows and columns, using the chaotic sequence LG1 as the row index sequence of the random number x generated in step S322, the method is as follows: O row (i)=mod(LG1(i)×10 12 ,M×N-i),i=0,1,…,M×N-1 Expand the plaintext image P matrix of size M×N into a one-dimensional array by row, and use the Knuth-Durstenfeld shuffle algorithm to scramble the rows; Then, the one-dimensional array after row scrambling is converted into a matrix, and the matrix is ​​expanded into a new one-dimensional array according to the columns. The chaotic sequence LG2 is used to generate the column index sequence according to the following formula: O column (i)=mod(LG2(i)×10 15 ,M×N-i),i=0,1,…,M×N-1 The Knuth-Durstenfeld shuffle algorithm is used again to shuffle the columns. The resulting one-dimensional array is converted into a matrix to obtain the scrambled image, which is denoted as P. D .

5. The image encryption method based on sine transform chaotic system according to claim 1 is characterized in that: In step S4, the diffusion steps are as follows: S41: The number of 2D-SGCS iterations is 1000+M×N. The results of the first 1000 iterations are discarded. The resulting chaotic sequences are called sg1 and sg2. The chaotic sequences sg1 and sg2 are processed as follows: S42: Generate random matrix R_P according to SG1 D And the scrambled matrix P D Perform XOR operation, R_P D The generated expression is as follows: R_P D1 (i) Transformed into D Matrix R_P with the same length and width D , the XOR operation is as follows: S43: In N_P D Select a point V(X, Y) in the matrix for self-diffusion. The selection formula is as follows: Taking point V(X, Y) as the center, perform XOR operation to the left. The formula is as follows: where i∈[1,X]; Taking point V(X, Y) as the center, perform XOR operation to the right. The formula is as follows: where i∈[1,MX]; Taking point V(X, Y) as the center, perform XOR operation upwards. The formula is as follows: where i∈[1,Y]; Taking point V(X, Y) as the center, perform XOR operation downwards. The formula is as follows: where i∈[1,NY]; After completing the diffusion in all directions, the ciphertext image C_P is obtained.

6. The image encryption method based on sine transform chaotic system according to claim 1 is characterized in that: In step S5, the encrypted image is decrypted according to the inverse operation of diffusion and scrambling. Since the operation of the diffusion part is an XOR operation, the decryption is performed again according to the center point. In the scrambling step of decryption, according to the index sequence O column (i) and O row (i) Perform column and row transformations on the scrambled matrix to finally obtain the plaintext image.

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