Color image encryption method based on hexagram model

Abstract

With the rapid development of network technology, the security of network information transmission is becoming more and more important. In order to solve the network transmission and storage security problems of image content, a color image encryption method based on the hexagram model is proposed. This method adopts the traditional scrambling-diffusion framework. In the scrambling stage, the Zigzag transformation is used to sort the pixel positions of the original image; in the diffusion stage, an image diffusion method is designed to change the pixel value by combining the characteristics of the hexagram structure and the 24 bits of the pixel. The experimental results show that this method can protect the original image content at the same time, with good encryption effect, strong security and high efficiency.

Description

Technical Field

[0001] The present invention relates to an information encryption technology, in particular to an image encryption method. Background Art

[0002] Nowadays, the rapid development of computer and network technology has brought about earth-shaking changes in people's lives, and various digital information has been widely used and disseminated. Among them, the application scenarios of multimedia information, especially digital images, involve many fields. Images can carry a lot of private information, and image information in special fields such as military and commerce has high requirements for confidentiality. Since images are easily illegally attacked by attackers when transmitted in the network, this information is leaked and tampered with, facing huge threats. Therefore, image encryption has become a hot issue in academia and industry.

[0003] Digital images are intuitive, vivid, vivid, informative, highly correlated, and highly redundant. To ensure the security of network storage and transmission of image content, a variety of image encryption methods have been proposed. However, current image encryption methods often have problems such as low encryption efficiency or weak security.

[0004] In order to protect the security of image network transmission and storage, a hexagram model was established, and a color image encryption method based on the hexagram model was proposed by using the defined pixel triangle and chaotic triangle for bit-level diffusion. This method combines the hexagram structure with the chaotic matrix to improve the efficiency and security of the encryption method. Summary of the invention

[0005] The purpose of the present invention is to propose a color image encryption method based on a hexagram model in view of the problems that the existing image encryption methods have low encryption efficiency or weak security.

[0006] Technical solution of the present invention: To achieve the above-mentioned invention object, the technical solution adopted is a color image encryption method based on the hexagram model. Let the sender be Alice and the receiver be Bob. Alice's encryption steps are described in detail as follows:

[0007] Step 1: Generate chaotic sequence: Let the original color image P 1 , whose size is m × n ×3, randomly select the initial value of the SET mapping shown in formula (1) x 0 and control parameters a , b and c ,

[0008] (1)

[0009] Among them, sin(·) is the sine function, ln(·) is the logarithmic function with constant e as the base, min{·} refers to the minimum function, x i ∈(0, 1), control parameter a , b ∈(0, 1) and c ∈(2, 3), iterate formula (1) 1000+ mn times and discard the first 1000 sequence values, we can get a sequence with a length of mn Chaotic sequence X= { x i};

[0010] Step 2: Integerization of chaotic sequence: Calculation,

[0011] y i =mod ( floor ( x i ×10 14 ), 256), (2)

[0012] in, x i ∈ X , mod (·) is the modulo operation function, floor (·) is a floor function; it can generate a length of mn Integer chaotic sequence Y= { y i};

[0013] Step 3: Convert decimal to binary: Y Each decimal element value in y i Convert to 8-bit binary number z i express, i =1, 2, …, mn , we can get a length of mn The binary vector Z = { z i};

[0014] Step 4: Intercept vector: Select according to certain rules z i The 5 bits in the sequence from high to low form a new binary number. w i , i =1, 2, …, mn , we can get a length of mn The binary vector W = { w i};

[0015] Step 5: Image scrambling: Perform Zigzag transformation on the three channels of the original image R, G and B respectively to change the pixel position and obtain the scrambled image P 2 ={ p 2 i};

[0016] Step 6: Establish a hexagram model: Each pixel position of a color image has 24 bits. These 24 bits are combined with the structural characteristics of a hexagram to establish a hexagram model. The specific operation is: 24 storage locations are set on the hexagram to store the 24 bits. The 24 designed locations are respectively at the 12 vertices of the hexagram, the center positions of the 6 triangles formed by it, and the midpoint positions of the 6 triangle bases. The 24 bits are stored in sequence from left to right and from top to bottom.

[0017] Step 7: Generate pixel triangles: In the hexagram model, 24 storage locations can be divided into triangles with six vertices, called pixel triangles. Each triangle has 5 storage locations that can store 5 bits, which are the three vertices of the triangle, the center position of the triangle, and the midpoint position of the base of the triangle. Adjacent triangles have a common critical point.

[0018] Step 8: Generate Chaotic Triangle: w i The 5 bits are stored in the triangle T i middle, i =1, 2, …, mn , called the chaotic triangle, T i The five storage locations are respectively at the three vertices of the triangle, the center of the triangle, and the midpoint of the base of the triangle;

[0019] Step 9: Pixel Diffusion: p 2 i The 24-bit values ​​of are stored in the hexagram model in sequence, and 6 pixel triangles are obtained. S 1 i , S 2 i , …, S 6i ,calculate:

[0020] (3)

[0021] in, r 1 i , r 2 i , …, r 6 i are the pixel triangles after diffusion, ⊕ represents XOR operation; in the hexagram model, r 1 i , r 2 i , …, r 6 i The 24 bits in the pixel are connected in order from top to bottom and from left to right to form a new pixel. p 3 i , i =1, 2, …, mn , we can get the diffusion image P 3 ={ p 3 i}, which is the encrypted image.

[0022] During the decryption process, the same chaotic sequence is used to encrypt the image. P 3 Perform decryption to restore the original image P 1 ; Bob’s decryption process is the reverse process of Alice’s encryption.

[0023] Beneficial effects: In view of the problems of low encryption efficiency or weak security in current image encryption methods, the present invention proposes a color image encryption method based on the hexagram model. The main contributions are as follows: (1) The hexagram structure characteristics are combined with the 24 bits of pixels to establish a hexagram model, and the defined pixel triangle and chaotic triangle are used for bit-level transformation to achieve diffusion in binary transformation to achieve the purpose of changing the pixel value size, thus solving the problem of the single diffusion transformation method in general; (2) Based on the established hexagram model, a color image encryption method based on the hexagram model is proposed; (3) Experimental results and method analysis show that the new method has good encryption effect, strong security and high efficiency, and can achieve network transmission and storage security of image content. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 : Flowchart of color image encryption based on hexagram model;

[0025] Figure 2 : original image;

[0026] Figure 3 : Schematic diagram of the hexagram model;

[0027] Figure 4 : Encrypted image. DETAILED DESCRIPTION

[0028] Figure 1 It is a color image encryption flow chart based on the hexagram model.

[0029] The programming software used is Matlab R2019b, arbitrarily selected Figure 2 Color image shown P 1 As the original image. Using the proposed color image encryption method based on the hexagram model, Alice's encryption process is detailed as follows.

[0030] Step 1: Generate chaotic sequence: Let the original color image P 1 , whose size is 512×512×3, and the initial value of the SET mapping shown in formula (1) is randomly selected x 0=0.637 and control parameters a =0.479, b =0.718 and c =2.013, iterate formula (1) 1000+512×512 times and discard the first 1000 sequence values, and you can get a chaotic sequence with a length of 512×512 X= { x i}.

[0031] Step 2: Integerization of chaotic sequence: Formula (2) can generate an integer chaotic sequence with a length of 512×512. Y= { y i}.

[0032] Step 3: Convert decimal to binary: Y Each decimal element value in y i Convert to 8-bit binary number z i express, i =1, 2, …, 512×512, we get a binary vector of length 512×512 Z = { zi}.

[0033] Step 4: Intercept vector: Select according to certain rules z i The 5 bits in the sequence from high to low form a new binary number. w i , i =1, 2, …, 512×512, we get a binary vector of length 512×512 W = { w i}.

[0034] Step 5: Image scrambling: Perform Zigzag transformation on the three channels of the original image R, G and B respectively to change the pixel position and obtain the scrambled image P 2 ={ p 2 i}.

[0035] Step 6: Establish a hexagram model: Each pixel position of the color image has 24 bits. These 24 bits are combined with the characteristics of the hexagram structure to establish a hexagram model, such as Figure 3 As shown; the specific operation is: set 24 storage locations on the hexagram to store 24 bits. The designed 24 locations are respectively at the 12 vertices of the hexagram, the center positions of the 6 triangles surrounded by it, and the midpoints of the 6 triangle bases. The 24 bits are stored in sequence from left to right and from top to bottom.

[0036] Step 7: Generate pixel triangles: In the hexagram model, 24 storage locations can be divided into triangles with six vertices, called pixel triangles. Each triangle has 5 storage locations that can store 5 bits, namely the three vertices of the triangle, the center position of the triangle, and the midpoint position of the base of the triangle. Adjacent triangles have a common critical point.

[0037] Step 8: Generate Chaotic Triangle: w i The 5 bits are stored in the triangle T i middle, i =1, 2, …,512×512, called a chaotic triangle, T i The five storage locations are respectively at the three vertices of the triangle, the center of the triangle, and the midpoint of the base of the triangle.

[0038] Step 9: Pixel Diffusion: p2 i The 24-bit values ​​of are stored in the hexagram model in sequence, and 6 pixel triangles are obtained. S 1 i , S 2 i , …, S 6 i , the calculated r 1 i , r 2 i , …, r 6 i The 24 bits in the pixel are connected in order from top to bottom and from left to right to form a new pixel. p 3 i , i =1, 2, …, 512×512, we can get the diffusion image P 3 ={ p 3 i}, which is the encrypted image, such as Figure 4 shown.

[0039] In the decryption process, the same chaotic sequence is used to decrypt the encrypted image to obtain the original image. Figure 2 As shown in Figure 2. Bob's decryption process is the reverse process of Alice's encryption.

Claims

1. A color image encryption method based on a hexagram model, characterized in that: The encryption process includes the following steps: Step 1: Generate chaotic sequence: Let the original color image P 1 , whose size is m × n ×3, randomly select the initial value of the SET mapping shown in formula (1) x 0 and control parameters a , b and c , （1） Among them, sin(·) is the sine function, ln(·) is the logarithmic function with constant e as the base, min{·} refers to the minimum function, x i ∈(0, 1), control parameter a , b ∈(0, 1) and c ∈(2, 3), iterate formula (1) 1000+ mn times and discard the first 1000 sequence values, we can get a sequence with a length of mn Chaotic sequence X= { x i }; Step 2: Integerization of chaotic sequence: Calculation, y i =mod ( floor ( x i ×10 14 ), 256)， （2） in, x i ∈ X , mod (·) is the modulo operation function, floor (·) is a floor function; it can generate a length of mn Integer chaotic sequence Y= { y i }; Step 3: Convert decimal to binary: Y Each decimal element value in y i Convert to 8-bit binary number z i express, i =1,2, …, mn , we can get a length of mn The binary vector Z = { z i }; Step 4: Intercept vector: Select according to certain rules z i The 5 bits in the sequence from high to low form a new binary number. w i , i =1, 2, …, mn , we can get a length of mn The binary vector W = { w i }; Step 5: Image scrambling: Perform Zigzag transformation on the three channels of the original image R, G and B respectively to change the pixel position and obtain the scrambled image P 2 ={ p 2 i }; Step 6: Establish a hexagram model: Each pixel position of a color image has 24 bits. These 24 bits are combined with the structural characteristics of a hexagram to establish a hexagram model. The specific operation is: 24 storage locations are set on the hexagram to store the 24 bits. The 24 designed locations are respectively at the 12 vertices of the hexagram, the center positions of the 6 triangles formed by it, and the midpoint positions of the 6 triangle bases. The 24 bits are stored in sequence from left to right and from top to bottom. Step 7: Generate pixel triangles: In the hexagram model, 24 storage locations can be divided into triangles with six vertices, called pixel triangles. Each triangle has 5 storage locations that can store 5 bits, which are the three vertices of the triangle, the center position of the triangle, and the midpoint position of the base of the triangle. Adjacent triangles have a common critical point. Step 8: Generate Chaotic Triangle: w i The 5 bits are stored in the triangle T i middle, i =1, 2, …, mn , called the chaotic triangle, T i The five storage locations are respectively at the three vertices of the triangle, the center of the triangle, and the midpoint of the base of the triangle; Step 9: Pixel Diffusion: p 2 i The 24-bit values ​​of are stored in the hexagram model in sequence, and 6 pixel triangles are obtained. S 1 i , S 2 i , …, S 6 i ,calculate: （3） in, r 1 i , r 2 i , …, r 6 i are the pixel triangles after diffusion, ⊕ represents XOR operation; in the hexagram model, r 1 i , r 2 i , …, r 6 i The 24 bits in the pixel are connected in order from top to bottom and from left to right to form a new pixel. p 3 i , i =1, 2, …, mn , we can get the diffusion image P 3 ={ p 3 i }, which is the encrypted image.

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