CN113674365B - Image blocking encryption method and system based on chaos and calculation hologram - Google Patents
Image blocking encryption method and system based on chaos and calculation hologram Download PDFInfo
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Abstract
The invention provides an image block encryption method and system based on chaos and calculation hologram, which solves the problem that the current image encryption mode cannot give consideration to encryption safety and encryption operation flexibility, firstly, three-channel decomposition is carried out on a plaintext image to be encrypted, three single-channel gray images are respectively divided into sub-images with the same size, partial sub-images are randomly selected, pseudo-random sequences are generated based on a hyper-chaos system, pixel scrambling is carried out on the sub-images respectively, then pixel diffusion is carried out, the scrambling and diffusion operations both increase the difficulty of decryption, in addition, the above processes use a block encryption technology, the encryption key space is larger, the effect is better, then the phase recovery GS algorithm in calculation hologram is utilized, the residual sub-images are converted into holograms, the process of converting the holograms is another encryption process, the operation in a computer system is easy, and the encryption operation flexibility is improved from another aspect.
Description
Technical Field
The invention relates to the technical field of image encryption, in particular to an image blocking encryption method and system based on chaos and calculation holography.
Background
In the twenty-first century, image information security has gradually become a focus of social attention, and in the process of storing, processing and transmitting, the image information is most likely to be intercepted, tampered and forged by a third party, and great threat is brought to the fields of business, military and scientific research. In the era of explosion of information, more and more digital images need to be stored and transferred more securely, and with the development of multimedia, the confidentiality of image information is also receiving more and more importance, so it is important and urgent to explore more efficient and safe image encryption methods.
Because the image has strong redundancy and strong correlation between adjacent pixels, the traditional encryption algorithms such as DES, AES and RSA are not suitable for image encryption and have low encryption efficiency. The chaos phenomenon is a deterministic and random-like process in a nonlinear dynamic system, and the chaos dynamics is rapidly developed on the basis, so that the chaos can be used as a new password system, and text, sound and image data can be encrypted. The principle of chaotic encryption is to perform specific operation on original information and a chaotic sequence generated by a chaotic generator, and decryption is to perform inverse operation on encrypted information and the chaotic sequence generated by the chaotic generator, so that the chaotic signal is removed, and the original information is converted into a random noise-like state, thereby encrypting the digital image file.
In 2018, 6 and 8 days, chinese patent (publication number: CN 108133447A) discloses a chaotic encryption method of a color image, wherein Px, py and Pz are used for scrambling three primary colors of the color image in a space domain range, so that the strength of algorithm diffusion is enhanced, and the decryption difficulty is further increased; the three primary color components are scrambled respectively, so that the encrypted image is visually changed in color, and the image is more difficult to read and understand; meanwhile, the scrambling degree of the algorithm used in the patent is similar to that of the magic square transformation, and the algorithm has good scrambling property and attack resistance, and the whole algorithm has slightly poorer operational flexibility due to high encryption security and complex process, so a method for combining encryption security and encryption operational flexibility is urgently sought.
Disclosure of Invention
In order to solve the problem that the current image encryption mode cannot achieve both encryption safety and encryption operation flexibility, the invention provides the image block encryption method and system for chaos and calculation holography, which use block encryption, have better encryption effect and simple operation, and can well ensure confidentiality and safety of image information in the using and transmitting processes.
In order to achieve the technical effects, the technical scheme of the invention is as follows:
an image block encryption method based on chaos and computation holography, the method at least comprising:
s1, carrying out three-channel RGB decomposition on a plaintext image to be encrypted to obtain three single-channel gray images;
s2, dividing three single-channel gray images into sub-images with the same Z block size, randomly selecting N sub-images, constructing a Lorenz hyperchaotic system, generating a pseudo-random sequence through the Lorenz hyperchaotic system, respectively carrying out pixel scrambling on the N sub-images, and then carrying out pixel diffusion;
s3, converting the residual Z-N block sub-images into holograms by using a phase recovery GS algorithm in the calculation hologram;
s4, splicing the N sub-images after pixel scrambling and diffusion and the Z-N sub-images after conversion into holograms into a complete single-channel encryption image, and synthesizing by utilizing three channels RGB to obtain the complete encryption image.
Preferably, the Lorenz hyper-chaotic system described in the step S2 is defined as:
w＝-yZ+rw
wherein a, b, c, r are parameters of the Lorenz hyper-chaotic system; x, y, z, w is a state variable of the Lorenz hyperchaotic system, and when a=10, b=8/3, c=28, r= -1, the system is in a chaotic state; pseudo-random sequence M generated by Lorenz hyperchaotic system 1 Converting N sub-images into one-dimensional vectors, and then respectively combining with a pseudo-random sequence M 1 And (3) performing pixel scrambling, wherein the pixel scrambling method is Arnold mapping scrambling.
Preferably, the formula for pixel scrambling using Arnold map scrambling is specifically:
wherein j and k are pixel points after pixel scrambling, and 1 and i are the number of N sub-pixel points; e, f is a pseudo-random variable, and is a positive integer.
Preferably, the way to convert the N-block sub-images into one-dimensional vectors is:
the N sub-images are first converted into an image matrix by using an imread function, and then the image matrix is converted into a one-dimensional vector by using a reshape function.
Preferably, in the step S2, the pixel diffusion method is an exclusive-or operation, and the formula for performing pixel diffusion through the exclusive-or operation is specifically:
wherein, C, S are both cipher vectors, C is a one-dimensional vector of the finally required encrypted image, P is a one-dimensional vector converted from the scrambled image, t=1, 2, …, MN is a pixel parameter; is an exclusive-or sign, and is diffused into C by each pixel in the exclusive-or operation P.
Here, P corresponds to a one-dimensional vector converted from the image scrambled in the previous step, that is, after the original image is subjected to pixel scrambling, a preliminary encrypted image is formed (the image is not resolved by the effective information after the pixel scrambling); then the primary encryption image is converted into a one-dimensional vector P by a matrix, and the integral diffusion of pixels is represented by an exclusive OR operation formula.
Preferably, the pixel is subjected to an exclusive OR operation before being diffused with a pseudo-random sequence M 1 The image that has undergone Arnold mapping pixel scrambling is again converted into a one-dimensional vector.
Preferably, the process of converting the remaining Z-N block sub-image into a hologram using the phase recovery GS algorithm in the computed hologram in step S3 is:
s31, setting a target image and a threshold value, and starting from a space domain, forming an initial input by a sub-image and a random phase matrix with the same size, wherein the sub-image is used as the amplitude of the initial input, and the random phase matrix is used as the phase of the initial input;
s32, carrying out Fourier transform on the initial input to obtain frequency domain distribution, then applying frequency domain constraint on the initial input in the frequency domain, normalizing the amplitude, replacing the amplitude by the target image, and reserving phase information;
s33, performing inverse Fourier transform on the normalized frequency domain distribution to obtain spatial domain distribution, and applying spatial constraint on the spatial domain distribution in the spatial domain;
s34, calculating a correlation coefficient between the target image and the image generated by the iteration, judging whether the correlation coefficient is greater than or equal to a threshold value, if so, ending the iteration to obtain a restored image of the sub-image and a corresponding phase hologram thereof, wherein the phase hologram is used as an encryption map, and the restored image is used as a decryption map; otherwise, the process returns to step S31.
Preferably, the correlation coefficient calculation formula in step S34 is:
where rr denotes a correlation coefficient, g (u, v) is a target image, g' (u, v) denotes an output image of a sub-image, M, N respectively denote the number of lines and the number of columns of the image, and the greater the correlation coefficient, the higher the degree of similarity of the target image and the hologram transformed by the sub-image.
The GS algorithm makes the iteration of sub-image back and forth between space domain and frequency domain make Fourier and inverse Fourier transform, and applies known constraint condition to space and frequency domain respectively, so as to maximally recover the phase distribution of image in space and frequency domain, and as the iteration number increases, the output image can gradually converge on the target image, when the error of the two meets the convergence threshold value, the iteration is completed, at this moment, the phase information obtained by space domain is the required phase distribution, and the sub-image is converted into hologram of pure phase information, which is itself encrypted, and the iteration number is less, the convergence speed is high, and the operation is simple.
Preferably, after obtaining the complete encrypted image, the reverse operations of steps S1 to S4 are performed to obtain the decrypted image.
The invention also provides an image block encryption system based on chaos and calculation hologram, which is used for realizing the image block encryption method based on chaos and calculation hologram, and comprises the following steps:
the three-channel RGB decomposition module is used for carrying out three-channel RGB decomposition on the plaintext image to be encrypted to obtain three single-channel gray maps;
the pixel scrambling and diffusing module is used for dividing three single-channel gray images into sub-images with the same Z block size respectively, randomly selecting N sub-images, constructing a Lorenz hyperchaotic system, generating a pseudo-random sequence through the Lorenz hyperchaotic system, carrying out pixel scrambling on the N sub-images respectively, and then carrying out pixel diffusion;
the holographic conversion module converts the residual Z-N sub-images into holograms by utilizing a phase recovery GS algorithm in the calculated holograms;
and the three-channel RGB synthesis module is used for splicing the N blocks of sub-images after pixel scrambling and diffusion and the Z-N blocks of sub-images converted into holograms into a complete single-channel encryption image, and the complete encryption image is obtained by utilizing three-channel RGB synthesis.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
the invention provides an image block encryption method and system based on chaos and calculation hologram, firstly, three-channel RGB decomposition is carried out on a plaintext image to be encrypted to obtain three single-channel gray images, the three single-channel gray images are respectively divided into sub-images with the same size, partial sub-images are randomly selected, a pseudo-random sequence is generated through a Lorenz hyperchaotic system, pixel scrambling is carried out on the sub-images respectively, then pixel diffusion is carried out, scrambling and diffusion operations are carried out, the difficulty of decoding is improved, in addition, the processes use a block encryption technology, the encryption key space is larger, the effect is better, then the phase recovery GS algorithm in calculation hologram is utilized, the residual sub-images are converted into holograms, the process of converting the holograms is another encryption process, compared with the process of simply relying on chaos encryption, the storage information amount is large, the operation is easy in a computer system, the encryption operation flexibility is improved from another layer, the sub-images after pixel scrambling and diffusion and the holographic converted sub-images are spliced into a complete single-channel encryption image, the three-channel RGB encryption is utilized, the complete encryption image can be obtained, and the security and the confidentiality and the security information can be well transmitted in the process.
Drawings
FIG. 1 shows a flow diagram of an image block encryption method based on chaos and computer generated hologram according to an embodiment of the present invention;
fig. 2 shows a system configuration diagram of an image block encryption method based on chaos and computer generated hologram according to an embodiment of the present invention.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the present patent;
for better illustration of the present embodiment, some parts of the drawings may be omitted, enlarged or reduced, and do not represent actual dimensions;
it will be appreciated by those skilled in the art that some well known descriptions in the figures may be omitted.
The positional relationship depicted in the drawings is for illustrative purposes only and is not to be construed as limiting the present patent;
the technical scheme of the invention is further described below with reference to the accompanying drawings and examples.
Examples
Considering that more and more digital images need to be stored and transferred more securely at present, and meanwhile, with the development of multimedia, the confidentiality of image information is also receiving more and more importance, as shown in fig. 1, the invention provides an image block encryption method based on chaos and computer generated hologram, referring to fig. 1, which comprises the following steps:
s1, carrying out three-channel RGB decomposition on a plaintext image to be encrypted to obtain three single-channel gray images; in this embodiment, the plaintext image to be encrypted is a 512×512 color image, and the step is based on a Matlab software platform, and three-channel RGB decomposition can be implemented through digital image processing, so as to obtain three single-channel gray images;
s2, respectively dividing three single-channel gray images into 4 sub-images with the same size, wherein the size is 256 x 256, and the total number of the sub-images is 12, randomly selecting N sub-images, constructing a Lorenz hyperchaotic system, generating a pseudo-random sequence through the Lorenz hyperchaotic system, respectively carrying out pixel scrambling on the N sub-images, and then carrying out pixel diffusion;
s3, converting the residual 4-N sub-images into holograms by using a phase recovery GS algorithm in the calculation hologram;
s4, splicing the N sub-images with the scrambled and diffused pixels and the sub-images with the 4-N converted holograms into a complete single-channel encrypted image, and synthesizing by utilizing three channels RGB to obtain the complete encrypted image.
In this embodiment, the Lorenz hyper-chaotic system in step S2 is defined as:
w＝-yZ+rw
wherein a, b, c, r are parameters of the Lorenz hyper-chaotic system; x, y, z, w is a state variable of the Lorenz hyperchaotic system, and when a=10, b=8/3, c=28, r= -1, the system is in a chaotic state; pseudo-random sequence M generated by Lorenz hyperchaotic system 1 Wherein, on the premise of constructing the Lorenz hyperchaotic system, the hyperchaotic system is utilized to generate a pseudo-random sequence M 1 The process of (1) belongs to a mature technology, and is not repeated, the N sub-images are converted into one-dimensional vectors, and then the one-dimensional vectors are respectively combined with a pseudo-random sequence M 1 And (5) carrying out pixel scrambling, wherein the pixel scrambling method is Arnold mapping scrambling.
In this embodiment, the formula for performing pixel scrambling using Arnold map scrambling is specifically:
wherein j and k are pixel points after pixel scrambling, and 1 and i are the number of N sub-pixel points; e, f is a pseudo-random variable, and is a positive integer.
Let x0, y0, z0, w0 be the initial values of the system, in this embodiment x0=1.0, y0=2.0, z0=3.0, w0=4.0.
In this embodiment, the manner of converting the N-block sub-images into one-dimensional vectors is as follows:
the N sub-images are first converted into an image matrix by using an imread function, and then the image matrix is converted into a one-dimensional vector by using a reshape function.
The pixel diffusion method in step S2 is an exclusive-or operation, and the formula for performing pixel diffusion through the exclusive-or operation specifically includes:
wherein, C, S are both cipher vectors, C is a one-dimensional vector of the finally required encrypted image, P is a one-dimensional vector converted from the scrambled image, t=1, 2, …, MN is a pixel parameter; is an exclusive-or sign, and is diffused into C by each pixel in the exclusive-or operation P. P corresponds to a one-dimensional vector converted from the image scrambled in the previous step, namely, after the original image is subjected to pixel scrambling, a preliminary encrypted image is formed (effective information cannot be distinguished from the image after the pixel scrambling); then the primary encryption image is converted into a one-dimensional vector P by a matrix, and the integral diffusion of pixels is represented by an exclusive OR operation formula: p is an input encrypted image one-dimensional vector, C, S is a password vector (S is a pseudo-random sequence generated by a chaotic system, and C is a finally required encrypted image one-dimensional vector); the first step is that P1 and C0 (C0 can be set as any number) and S1 are subjected to exclusive OR operation to obtain C1; the second step is that P2 is exclusive-OR' ed with C1, S2, and so on, to get C2 …, and each pixel of P can be diffused into C.
In the present embodiment, the pixel diffusion is preceded by an exclusive OR operation with the pseudo-random sequence M 1 The image that has undergone Arnold mapping pixel scrambling is again converted into a one-dimensional vector.
In this embodiment, the process of converting the remaining Z-N block sub-images into holograms using the phase recovery GS algorithm in the computed hologram in step S3 is as follows:
s31, setting a target image and a threshold value, and starting from a space domain, forming an initial input by a sub-image and a random phase matrix with the same size, wherein the sub-image is used as the amplitude of the initial input, and the random phase matrix is used as the phase of the initial input;
s32, carrying out Fourier transform on the initial input to obtain frequency domain distribution, then applying frequency domain constraint on the initial input in the frequency domain, normalizing the amplitude, replacing the amplitude by the target image, and reserving phase information;
s33, performing inverse Fourier transform on the normalized frequency domain distribution to obtain spatial domain distribution, and applying spatial constraint on the spatial domain distribution in the spatial domain;
s34, calculating a correlation coefficient between the target image and the image generated by the iteration, judging whether the correlation coefficient is greater than or equal to a threshold value, if so, ending the iteration to obtain a restored image of the sub-image and a corresponding phase hologram thereof, wherein the phase hologram is used as an encryption map, and the restored image is used as a decryption map; otherwise, the process returns to step S31.
The iteration here is to ensure that the decrypted image is as close as possible to the original image, and thus the target image (i.e., the original image) and the restored image (i.e., the decrypted image).
In this embodiment, the correlation coefficient calculation formula in step S34 is as follows:
where rr denotes a correlation coefficient, g (u, v) is a target image, g' (u, v) denotes an output image of a sub-image, M, N respectively denote the number of lines and the number of columns of the image, and the greater the correlation coefficient, the higher the degree of similarity of the target image and the hologram transformed by the sub-image.
The GS algorithm is proposed by Gerchberg and Saxton in 1971, and the mathematical derivation formula is as follows:
G n (u，v)＝F[g n-1 (x，y)]
the value range of the random phase matrix is 0-2 pi, wherein x and y are the transverse and longitudinal coordinates of a space domain, u and v are the transverse and longitudinal coordinates of a frequency domain, F is Fourier transform, F -1 Is inverse Fourier transform, G n (u, v) is the coordinates of the image after the nth transformation in the frequency domain, g n-1 And (x, y) is the coordinates of the image in the space domain after the n-1 th transformation, and k is the range of 0-1 of feedback parameters. The GS algorithm makes the iteration of the sub-image back and forth between the space domain (airspace) and the frequency domain carry out Fourier transform and inverse Fourier transform, and known constraint conditions are respectively applied to the space domain and the frequency domain, so that the phase distribution of the image in the space domain and the frequency domain is recovered to the greatest extent, the output image gradually converges on the target image along with the increase of the iteration times, when the error of the two images meets the convergence threshold value, the iteration is ended, the phase information obtained in the airspace is the required phase distribution, the sub-image is converted into a hologram with pure phase information, the hologram is encrypted, the iteration times are less, the convergence speed is high, and the operation is simple to realize.
In this embodiment, the final step combines the four sub-encrypted images of a single channel into a complete single-channel encrypted image, and synthesizes the three channel encrypted images into a three channel synthesizing method based on Matlab.
After obtaining the complete encrypted image, the reverse operation of steps S1-S4 is executed to obtain the decrypted image.
As shown in fig. 2, the present invention further provides an image block encryption system based on chaos and computation hologram, where the system is used to implement the image block encryption method based on chaos and computation hologram, and the method includes:
the three-channel RGB decomposition module is used for carrying out three-channel RGB decomposition on the plaintext image to be encrypted to obtain three single-channel gray maps;
the pixel scrambling and diffusing module is used for dividing three single-channel gray images into sub-images with the same Z block size respectively, randomly selecting N sub-images, constructing a Lorenz hyperchaotic system, generating a pseudo-random sequence through the Lorenz hyperchaotic system, carrying out pixel scrambling on the N sub-images respectively, and then carrying out pixel diffusion;
the holographic conversion module converts the residual Z-N sub-images into holograms by utilizing a phase recovery GS algorithm in the calculated holograms;
and the three-channel RGB synthesis module is used for splicing the N blocks of sub-images after pixel scrambling and diffusion and the Z-N blocks of sub-images converted into holograms into a complete single-channel encryption image, and the complete encryption image is obtained by utilizing three-channel RGB synthesis.
In summary, the invention proposes to firstly perform three-channel decomposition on a color original image, respectively divide three single-channel gray level images into 4 sub-images, perform Arnold matrix scrambling and exclusive OR operation diffusion on N sub-images by using a random sequence generated by a Lorenz hyper-chaotic system, finally encode other 4-N Zhang Zitu images into holograms by using a GS calculation holographic technology, and finally splice the encrypted sub-images into a complete encrypted image, so that the image block encryption is completed, the encryption effect is better, the key space is larger, and the confidentiality and the security of image information in the use and transmission process can be well ensured.
It is to be understood that the above examples of the present invention are provided by way of illustration only and are not intended to limit the scope of the invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.
Claims (8)
1. An image block encryption method based on chaos and computation hologram, which is characterized in that the method at least comprises the following steps:
s1, carrying out three-channel RGB decomposition on a plaintext image to be encrypted to obtain three single-channel gray images;
s2, dividing three single-channel gray images into sub-images with the same Z block size, randomly selecting N sub-images, constructing a Lorenz hyperchaotic system, generating a pseudo-random sequence through the Lorenz hyperchaotic system, respectively carrying out pixel scrambling on the N sub-images, and then carrying out pixel diffusion;
the Lorenz hyper-chaotic system described in the step S2 is defined as:
w＝-yz+rw
wherein a, b, c, r are parameters of the Lorenz hyper-chaotic system; x, y, z, w is a state variable of the Lorenz hyperchaotic system, and when a=10, b=8/3, c=28, r= -1, the system is in a chaotic state; pseudo-random sequence M generated by Lorenz hyperchaotic system 1 Converting N sub-images into one-dimensional vectors, and then respectively combining with a pseudo-random sequence M 1 The pixel scrambling is performed such that the pixel scrambling,the pixel scrambling method is Arnold mapping scrambling;
s3, converting the residual Z-N block sub-images into holograms by using a phase recovery GS algorithm in the calculation hologram;
in step S3, the process of converting the remaining Z-N block sub-images into holograms using the phase recovery GS algorithm in the computed hologram is as follows:
s31, setting a target image and a threshold value, and starting from a space domain, forming an initial input by a sub-image and a random phase matrix with the same size, wherein the sub-image is used as the amplitude of the initial input, and the random phase matrix is used as the phase of the initial input;
s32, carrying out Fourier transform on the initial input to obtain frequency domain distribution, then applying frequency domain constraint on the initial input in the frequency domain, normalizing the amplitude, replacing the amplitude by the target image, and reserving phase information;
s33, performing inverse Fourier transform on the normalized frequency domain distribution to obtain spatial domain distribution, and applying spatial constraint on the spatial domain distribution in the spatial domain;
s34, calculating a correlation coefficient between the target image and the image generated by the iteration, judging whether the correlation coefficient is greater than or equal to a threshold value, if so, ending the iteration to obtain a restored image of the sub-image and a corresponding phase hologram thereof, wherein the phase hologram is used as an encryption map, and the restored image is used as a decryption map; otherwise, returning to the step S31;
s4, splicing the N sub-images after pixel scrambling and diffusion and the Z-N sub-images after conversion into holograms into a complete single-channel encryption image, and synthesizing by utilizing three channels RGB to obtain the complete encryption image.
2. The image block encryption method based on chaos and computation hologram according to claim 1, wherein the formula for pixel scrambling by Arnold mapping scrambling is specifically:
wherein j and k are pixel points after pixel scrambling, and 1 and i are the number of N sub-pixel points; e, f is a pseudo-random variable, and is a positive integer.
3. The image block encryption method based on chaos and computation hologram according to claim 2, wherein the way of converting N sub-images into one-dimensional vectors is:
the N sub-images are first converted into an image matrix by using an imread function, and then the image matrix is converted into a one-dimensional vector by using a reshape function.
4. The image block encryption method based on chaos and computation hologram according to claim 3, wherein the pixel diffusion method in step S2 is an exclusive-or operation, and the formula for pixel diffusion by the exclusive-or operation is specifically:
wherein, C, S are both cipher vectors, C is a one-dimensional vector of the finally required encrypted image, P is a one-dimensional vector converted from the scrambled image, t=1, 2, …, MN is a pixel parameter; is an exclusive-or sign, and is diffused into C by each pixel in the exclusive-or operation P.
5. The image block encryption method based on chaos and computation of hologram according to claim 4, characterized by the fact that it is combined with a pseudo-random sequence M before pixel diffusion by exclusive-or operation 1 The image that has undergone Arnold mapping pixel scrambling is again converted into a one-dimensional vector.
6. The image block encryption method based on chaos and computation hologram according to claim 1, wherein the correlation coefficient computation formula in step S34 is:
where rr denotes a correlation coefficient, g (u, v) is a target image, g' (u, v) denotes an output image of a sub-image, M, N denote the number of lines and the number of columns of the image, respectively, and the greater the correlation coefficient, the higher the degree of similarity between the target image and a restored image of the sub-image.
7. The image block encryption method based on chaos and computation hologram according to claim 1, wherein after obtaining a complete encrypted image, the reverse operations of steps S1 to S4 are performed to obtain a decrypted image.
8. An image block encryption system based on chaos and computation hologram, characterized in that the system is used for realizing the image block encryption method based on chaos and computation hologram as claimed in claim 1, the system comprises:
the three-channel RGB decomposition module is used for carrying out three-channel RGB decomposition on the plaintext image to be encrypted to obtain three single-channel gray maps;
the pixel scrambling and diffusing module is used for dividing three single-channel gray images into sub-images with the same Z block size respectively, randomly selecting N sub-images, constructing a Lorenz hyperchaotic system, generating a pseudo-random sequence through the Lorenz hyperchaotic system, carrying out pixel scrambling on the N sub-images respectively, and then carrying out pixel diffusion;
the Lorenz hyper-chaotic system is defined as follows:
w＝-yz+rw
wherein a, b, c, r are parameters of the Lorenz hyper-chaotic system; x, y, z, w is a state variable of the Lorenz hyperchaotic system, and when a=10, b=8/3, c=28, r= -1, the system is in a chaotic state; pseudo-random sequence M generated by Lorenz hyperchaotic system 1 Converting N sub-images into one-dimensional vectors, and then respectively combining with a pseudo-random sequence M 1 Performing pixel scrambling, wherein the pixel scrambling method is Arnold mapping scrambling;
the holographic conversion module converts the residual Z-N sub-images into holograms by utilizing a phase recovery GS algorithm in the calculated holograms;
the process of converting the remaining Z-N block sub-images into holograms using the phase recovery GS algorithm in the computed hologram is:
s31, setting a target image and a threshold value, and starting from a space domain, forming an initial input by a sub-image and a random phase matrix with the same size, wherein the sub-image is used as the amplitude of the initial input, and the random phase matrix is used as the phase of the initial input;
s32, carrying out Fourier transform on the initial input to obtain frequency domain distribution, then applying frequency domain constraint on the initial input in the frequency domain, normalizing the amplitude, replacing the amplitude by the target image, and reserving phase information;
s33, performing inverse Fourier transform on the normalized frequency domain distribution to obtain spatial domain distribution, and applying spatial constraint on the spatial domain distribution in the spatial domain;
s34, calculating a correlation coefficient between the target image and the image generated by the iteration, judging whether the correlation coefficient is greater than or equal to a threshold value, if so, ending the iteration to obtain a restored image of the sub-image and a corresponding phase hologram thereof, wherein the phase hologram is used as an encryption map, and the restored image is used as a decryption map; otherwise, returning to the step S31;
and the three-channel RGB synthesis module is used for splicing the N blocks of sub-images after pixel scrambling and diffusion and the Z-N blocks of sub-images converted into holograms into a complete single-channel encryption image, and the complete encryption image is obtained by utilizing three-channel RGB synthesis.
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