Image encryption method and system based on coupled map lattices

Abstract

The application relates to the technical field of image encryption, in particular to an image encryption method and system based on a coupled mapping lattice. A key is obtained first to generate a coupled mapping lattice; then, 12 pseudo-random sequences in the coupled mapping lattice are extracted according to a plaintext image; one of the 12 pseudo-random sequences is selected to randomly group the remaining 11 pseudo-random sequences; bit layer image scrambling operations are performed on 8 groups of the pseudo-random sequences in the random groups; diffusion operations are performed on the remaining 3 groups of the pseudo-random sequences in the random groups; finally, the pseudo-random sequences obtained in steps S4 and S5 are combined to obtain an encrypted ciphertext image; the coupled mapping lattice is adopted to associate the permutation and diffusion operations, and the bit layer image is subjected to the scrambling and diffusion operations to realize the image encryption.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of image encryption technology, in particular to an image encryption method and system based on coupled mapping lattices. BACKGROUND

[0002] With the major changes of Internet of Things, big data and other technologies, digital image transmission and acquisition are widely used in military, medical, education, business and other fields, and the security, integrity and anti-interference of digital images are particularly important. The effective method for this is image encryption processing.

[0003] The encryption method for images mainly converts the image into a uniform distribution signal similar to noise irrelevant to the original image through a key, and when the receiver does not obtain the correct key, accurate image information cannot be obtained.

[0004] In order to protect important images and private images, people have proposed various encryption methods, but the existing methods are mostly based on low-dimensional chaotic mapping, and the key space and system parameters are small, which are not very secure for image encryption. SUMMARY

[0005] The technical problem solved by the present application is to provide an image encryption method based on coupled mapping lattices, which uses coupled mapping lattices to associate permutation and diffusion operations, and performs scrambling and diffusion operations on bit-level images to realize image encryption. An image encryption system based on coupled mapping lattices is also provided.

[0006] To solve the above technical problems, one technical solution adopted by the present application is to provide an image encryption method based on coupled mapping lattices, comprising the following steps:

[0007] Step S1, obtaining a key to generate a coupled mapping lattice;

[0008] Step S2, extracting 12 pseudo-random sequences in the coupled mapping lattice according to the plaintext image;

[0009] Step S3, selecting one of the 12 pseudo-random sequences to randomly group the remaining 11 pseudo-random sequences;

[0010] Step S4, performing bit-level image scrambling operation on the 8 groups of pseudo-random sequences in the random grouping;

[0011] Step S5, performing diffusion operation on the remaining 3 groups of pseudo-random sequences in the random grouping;

[0012] Step S6, merging the pseudo-random sequences obtained in steps S4 and S5 to obtain the encrypted ciphertext image.

[0013] As an improvement of the present application, in step S1, the key is obtained by calculating the Hash function.

[0014] As a further improvement of the present application, in step S2, the pseudo-random sequences in the coupled map lattice are extracted as the basis for grouping the permutation-diffusion pseudo-random sequences.

[0015] As a further improvement of the present application, in step S3, one of the 12 pseudo-random sequences is selected to randomly group the remaining 11 pseudo-random sequences, and the remaining 11 groups of pseudo-random sequences are divided into 8 groups of permutation sequences and 3 groups of diffusion sequences.

[0016] As a further improvement of the present application, in step S4, the 8 groups of permutation sequences are spliced to obtain an image, and the image is further decomposed into a bit layer image, and a one-dimensional array of the bit layer image is permuted to obtain an image array.

[0017] As a further improvement of the present application, in step S5, the 3 groups of diffusion sequences are converted into a two-dimensional array with the same dimension as the image array obtained in step S4.

[0018] As a further improvement of the present application, in step S5, the image array obtained in step S4 and the two-dimensional array obtained in step S5 are combined to obtain an encrypted ciphertext image.

[0019] An image encryption system based on a coupled map lattice, comprising:

[0020] A generation module for obtaining a key and generating a coupled map lattice;

[0021] An extraction module for extracting 12 pseudo-random sequences in the coupled map lattice according to a plaintext image;

[0022] A grouping module for grouping the pseudo-random sequences;

[0023] A permutation module for performing a bit layer image permutation operation on the pseudo-random sequences;

[0024] A diffusion module for performing a diffusion operation on the pseudo-random sequences;

[0025] An encryption module for merging and re-encrypting the pseudo-random sequences after the permutation and diffusion operations.

[0026] The present application has the following advantages: compared with the prior art, the present application uses a coupled map lattice to associate permutation and diffusion operations, and the present application realizes image encryption by performing permutation and diffusion operations on a bit layer image. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a step block diagram of the present application;

[0028] Figure 2 A flowchart of the present application;

[0029] Figure 3 A LSS coupled map lattice trajectory diagram of the present application;

[0030] Figure 4 A comparison diagram of the present application of plaintext image and encrypted image. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0032] Please refer to Figures 1 to 4 The present application is an image encryption method based on coupled map lattice, comprising the following steps:

[0033] Step S1, obtaining a key to generate a coupled map lattice;

[0034] Step S2, extracting 12 pseudo-random sequences in the coupled map lattice according to a plaintext image;

[0035] Step S3, selecting one of the 12 pseudo-random sequences to randomly group the remaining 11 pseudo-random sequences;

[0036] Step S4, performing a bit layer image scrambling operation on the 8 groups of pseudo-random sequences in the random grouping;

[0037] Step S5, performing a diffusion operation on the remaining 3 groups of pseudo-random sequences in the random grouping;

[0038] Step S6, merging the pseudo-random sequences obtained in steps S4 and S5 to obtain an encrypted ciphertext image.

[0039] The present application uses a coupled map lattice to associate permutation and diffusion operations, and realizes image encryption results by performing scrambling and diffusion operations on bit layer images.

[0040] In step S1, the key is obtained by calculating a Hash function to generate a coupled map lattice; specifically, a Logistic-Sine (LSS) type chaotic mapping is selected, which is an improved one-dimensional chaotic system LSS based on Logistic mapping and Sine mapping. Through dynamic analysis, it is known that, compared with one-dimensional simple chaotic systems, LSS has better chaotic characteristics and is more suitable for image encryption. The LSS chaotic system is described as follows:

[0041] X(i+1) = mod(rX(i)(1-X(i)) + (4-r)sin(πX(i)) / 4, 1) (Formula 1)

[0042] where r ∈ (0, 4), X n ∈ (0, 1).

[0043] Coupled Map Lattices (CML) is a typical dynamic system with discrete time, discrete space and continuous state, which is described as follows:

[0044]

[0045] where = 1, 2, 3, 4… is the time coordinate; i = 1, 2, 3, 4, …, L is the lattice position, L represents the length of CML; ε ∈ (0, 1) is the coupling strength factor, and satisfies the periodic boundary condition x n (0) = x n (L), x n (i) represents the state value of the i-th lattice at time n.

[0046] The color image F contains RGB three-channel data, which is decomposed into 24 bit images {F1, F2, … F 24 The bit value in each bit level image is brought into the following (Formula 3) to obtain the initial values X1(0), X2(0) … X 12 (0) of the coupled map lattices at different levels.

[0047] The key parameters r of the chaotic sequence X n and the key parameters ε of the coupled map lattices are obtained by using the Hash function, and the chaotic sequence X1 is obtained by iteratively calculating L+M×3N times according to (Formula 2), where L = 1000, and the NCA type coupled map lattices X = {X1, X2, …, X 12} are obtained by calculating according to (Formula 1), and finally each group of pseudo-random sequences [L+1, L+M×3N] is taken as the coupled map lattices for image scrambling, and the length of each sub-sequence is M×3N;

[0048] X i (0) = mod(∑(F 2i-1 +F 2i ) / 2, M×3N) (Formula 3).

[0049] In step S2, the pseudo-random sequences in the coupled map lattices are extracted as the basis for grouping the scrambling-diffusion pseudo-random sequences; specifically, e is calculated according to the following (Formula 4) first, and the pseudo-random sequences X eThe remaining 11 groups of pseudo-random sequences are divided into 8 groups of scrambling sequences {Z1, Z2,..., Z8} and 3 groups of diffusion sequences {K1, K2, K3} as the scrambling-diffusion pseudo-random sequence grouping basis;

[0050]

[0051] In step S3, one of the 12 pseudo-random sequences is selected to randomly group the remaining 11 pseudo-random sequences, and the remaining 11 groups of pseudo-random sequences are divided into 8 groups of scrambling sequences and 3 groups of diffusion sequences.

[0052] In step S4, the 8 groups of scrambling sequences are spliced to obtain an image, and the image is decomposed into bit layer images, and the one-dimensional array of the bit layer images is scrambled to obtain an image array; specifically, the RGB three channels of the MxN color image are spliced in turn according to the following (formula 5) to obtain an Mx3N image; then the image is decomposed into bit layer images {F B1 ,F B2 ,…F B8}, and converted into a one-dimensional array {S1, S1,..., S8} according to the column priority principle; the scrambling sequence Z i is sorted to obtain a new ordered sequence ZP = {ZP1, ZP2,..., ZP8}, and the position of the value of the sequence Z i in the sequence ZP i is recorded to obtain a sequence number representation ZT = {ZT1, ZT2,..., ZT8}, wherein ZP i (j) = X i (ZT(j)); finally, the bits Figure 1 one-dimensional array {S1, S1,..., S8} is scrambled according to the order of ZT = {ZT1, ZT2,..., ZT8} to obtain the scrambled array {S1', S'2,..., S8'}; and the inverse operation is converted into an Mx3N image array F';

[0053] F B (1:M,1:N) = F R (1:M,1:N)

[0054] F B (1:M,N+1:2N) = F G (1:M,1:N)

[0055] F B (1:M,2N+1:3N) = F B (1:M,1:N) (formula 5).

[0056] In step S5, the three groups of diffusion sequences are converted into two-dimensional arrays with the same dimension as the image array obtained in step S4; specifically, the image array obtained in step S4 is combined with the two-dimensional array obtained in step S5 to obtain an encrypted ciphertext image; and the diffusion pseudo-random sequence {K1, K2, K3} with a size of M*3N is converted into a two-dimensional array with the same dimension as the image F', and the RGB three-channel data is XORed according to the following (formula 6) to obtain an encrypted image G.

[0057]

[0058] The application further provides an image encryption system based on a coupled mapping lattice, comprising:

[0059] A generating module is configured to obtain a key and generate a coupled mapping lattice.

[0060] An extracting module is configured to extract 12 pseudo-random sequences in the coupled mapping lattice according to a plaintext image.

[0061] A grouping module is configured to group the pseudo-random sequences.

[0062] A scrambling module is configured to perform a bit-layer image scrambling operation on the pseudo-random sequences.

[0063] A diffusion module is configured to perform a diffusion operation on the pseudo-random sequences.

[0064] An encryption module is configured to combine and re-encrypt the pseudo-random sequences after the scrambling and diffusion operations.

[0065] In the application, the bit-layer image is scrambled and diffused to realize image encryption; the image encryption of the application belongs to symmetric encryption, and the decryption system is completely the same as the encryption system; by reversing the steps of the application to process the encrypted image, a decrypted image can be obtained.

[0066] The above description is merely an embodiment of the application, and does not limit the patent scope of the application; any equivalent structure or equivalent process transformation according to the content of the specification and drawings, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the application.

Claims

1. An image encryption method based on coupled map lattices, characterized in that, The method comprises the following steps: Step S1, obtaining a key and generating a coupled mapping lattice; Step S2, extracting 12 pseudo-random sequences in the coupled mapping lattice according to a plaintext image; Step S3, selecting one of the 12 pseudo-random sequences to randomly group the remaining 11 pseudo-random sequences; Step S4, performing a bit layer image scrambling operation on the 8 groups of pseudo-random sequences in the random grouping; Step S5, performing a diffusion operation on the remaining 3 groups of pseudo-random sequences in the random grouping; Step S6, merging the pseudo-random sequences obtained in steps S4 and S5 to obtain an encrypted ciphertext image; In step S2, the pseudo-random sequences in the coupled mapping lattice are extracted as the basis for scrambling-diffusion pseudo-random sequence grouping; In step S3, one of the 12 pseudo-random sequences is selected to randomly group the remaining 11 pseudo-random sequences, and the remaining 11 groups of pseudo-random sequences are divided into 8 groups of scrambling sequences and 3 groups of diffusion sequences; In step S4, the 8 groups of scrambling sequences are spliced to obtain an image, which is then decomposed into a bit layer image, and a one-dimensional array of the bit layer image is scrambled to obtain an image array.

2. The image encryption method based on coupled map lattices according to claim 1, wherein, In step S1, the key is obtained by calculating a Hash function.

3. The image encryption method based on coupled map lattices according to claim 2, characterized in that, In step S5, the 3 groups of diffusion sequences are converted into two-dimensional arrays with the same dimensions as the image array obtained in step S4.

4. The image encryption method based on coupled map lattices according to claim 3, characterized in that, In step S5, the image array obtained in step S4 and the two-dimensional array obtained in step S5 are merged to obtain an encrypted ciphertext image.

5. A coupled map lattice based image encryption system using the coupled map lattice based image encryption method of claim 1, characterized in that, The method comprises the following steps: A generating module is configured to obtain a key and generate a coupled mapping lattice; An extracting module is configured to extract 12 pseudo-random sequences in the coupled mapping lattice according to a plaintext image; A grouping module is configured to group the pseudo-random sequences; A scrambling module is configured to perform a bit layer image scrambling operation on the pseudo-random sequences; A diffusion module is configured to perform a diffusion operation on the pseudo-random sequences; An encryption module is configured to merge and re-encrypt the pseudo-random sequences after the scrambling and diffusion operations.

Images