Image encryption and decryption method and system based on linear polarization multiplexing metasurface

Abstract

The application provides an image encryption and decryption method and system based on a line polarization multiplexing super surface. The method comprises the following steps: obtaining an original image; using a double XOR algorithm to obtain a cipher image and a cipher book image according to a matrix of the original image and a matrix of a preset digital image; using electromagnetic waves of a first polarization direction and a second polarization direction to irradiate a line polarization multiplexing super surface respectively; using phase distributions of the cipher book image and the key image to load the cipher book image to the first polarization direction and load the key image to the second polarization direction, and sending the images to a receiving end; and the first polarization direction and the second polarization direction are perpendicular. The technical scheme of the application is advantageous to improve the quality of image transmission because the two polarization directions are perpendicular. The security is improved significantly because the cipher book image and the key image are based on the original image and skillfully use the digital image and the double XOR algorithm.

Description

Technical Field

[0001] This invention relates to the field of image encryption technology, and in particular to an image encryption and decryption method and system based on a linearly polarized multiplexed metasurface. Background Technology

[0002] Current image encryption technologies rely solely on software to encrypt images. If the encryption algorithm is cracked, the image will be leaked. This software-based approach to image encryption is inherently insecure and has significant drawbacks. Image transmission uses electromagnetic waves as the transmission medium, and the sending and receiving of these waves are achieved through metasurfaces. Polarization is a crucial parameter of electromagnetic waves; controlling the polarization allows more information to be loaded onto the same metasurface. Current technologies do not fully utilize the physical properties of metasurfaces and the polarization characteristics of electromagnetic waves, relying solely on image encryption and decryption algorithms. This results in low security for image processing and transmission. If an image is intercepted during transmission and decrypted using an algorithm, it can be easily cracked, posing a significant risk of data leakage. Summary of the Invention

[0003] A brief overview of the invention is given below to provide a basic understanding of certain aspects of it. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0004] In view of this, the present invention provides an image encryption and decryption method and system based on linearly polarized multiplexed metasurfaces, so as to at least solve the problem of low security caused by relying solely on software technology to encrypt images in the prior art.

[0005] According to one aspect of the present invention, an image encryption method based on a linearly polarized multiplexed metasurface is provided, comprising: acquiring an original image;

[0006] Based on the matrix of the original image and the matrix of the pre-set digital image, a double XOR algorithm is used to obtain the key image and the codebook image;

[0007] The digital image is used to display numbers, and the numbers are used to assist in encryption and decryption.

[0008] The phase distribution of the key image and the codebook image is determined based on the key image and the codebook image;

[0009] The phase distributions of the key image and the codebook image are loaded onto a linearly polarized multiplexed metasurface;

[0010] The linearly polarized multiplexed metasurface is irradiated with electromagnetic waves of the first polarization direction and the second polarization direction, respectively. Utilizing the phase distribution of the key image and the codebook image, the codebook image is loaded onto the first polarization direction, and the key image is loaded onto the second polarization direction, and then sent to the receiving end.

[0011] The first polarization direction is perpendicular to the second polarization direction.

[0012] Secondly, the present invention also provides an image decryption method based on a linearly polarized multiplexed metasurface, comprising:

[0013] Electromagnetic waves with first and second polarization directions are received based on a linearly polarized multiplexed metasurface.

[0014] The electromagnetic wave in the first polarization direction carries the key image, and the electromagnetic wave in the second polarization direction carries the codebook image.

[0015] The original image is obtained by using a double XOR decryption algorithm based on the key image and the codebook image;

[0016] Wherein, the first polarization direction is perpendicular to the second polarization direction.

[0017] Thirdly, this application proposes an image encryption and decryption system based on a linearly polarized multiplexed metasurface, including a transmitter and a receiver;

[0018] The transmitting end is used to employ the steps of the image encryption method based on linearly polarized multiplexed metasurfaces as described in any of the above-mentioned embodiments;

[0019] The receiving end is used to employ the steps of the image decryption method based on linearly polarized multiplexed metasurfaces as described in any of the above embodiments.

[0020] The technical solution of this application loads the codebook image onto an electromagnetic wave with a first polarization direction and the key image onto an electromagnetic wave with a second polarization direction. Since the two polarization directions are perpendicular, the mutual interference between the codebook image and the key image during transmission is reduced, which is beneficial to improving the quality of image transmission. Since the codebook image and the key image are based on the original image, the digital image is cleverly utilized, matrix transformation is employed, and a double XOR algorithm is used. Through careful design, the receiving end can restore the original image based on the codebook image and the key image, which significantly improves security.

[0021] These and other advantages of the invention will become more apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0022] The present invention can be better understood by referring to the description given below in conjunction with the accompanying drawings, in which the same or similar reference numerals are used throughout the drawings to denote the same or similar parts. These drawings, together with the following detailed description, are incorporated in and form part of this specification, and are used to further illustrate preferred embodiments of the invention and explain the principles and advantages of the invention. In the drawings:

[0023] Figure 1 This is a flowchart illustrating the image encryption method based on linearly polarized multiplexed metasurfaces according to the present invention;

[0024] Figure 2 This is a phase distribution diagram illustrating the present invention;

[0025] Figure 3 This illustrates the combined phase distribution diagram of the present invention;

[0026] Figure 4 This is a diagram illustrating the metasurface of the present invention;

[0027] Figure 5 This is a structural diagram illustrating the metasurface unit of the present invention;

[0028] Figure 6 This is a phase diagram illustrating the structure of the metasurface unit of the present invention;

[0029] Figure 7 This is a frequency amplitude phase diagram of the metasurface unit of the present invention;

[0030] Figure 8 This is a flowchart illustrating the image decryption method based on linearly polarized multiplexed metasurfaces according to the present invention;

[0031] Figure 9 These are images illustrating the entire decryption process of this invention;

[0032] Figure 10 It is a holographic image showing the entire decryption process of the present invention.

[0033] Those skilled in the art will understand that the elements in the accompanying drawings are shown for simplicity and clarity only, and are not necessarily drawn to scale. For example, the dimensions of some elements in the drawings may be enlarged relative to other elements to aid in understanding the embodiments of the invention. Detailed Implementation

[0034] Exemplary embodiments of the invention will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the development of any such actual embodiment to achieve the developer's specific goals, such as complying with constraints related to the system and business, and these constraints may vary depending on the implementation. Furthermore, it should be understood that while development work can be very complex and time-consuming, such development work is merely a routine task for those skilled in the art who benefit from this disclosure.

[0035] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the device structure and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0036] Firstly, this application proposes an image encryption method based on a linearly polarized multiplexed metasurface, see Appendix. Figure 1 It includes the following steps:

[0037] In step S102, the original image is obtained.

[0038] In step S104, the key image and the codebook image are obtained by using a double XOR algorithm based on the matrix of the original image and the matrix of the pre-set digital image.

[0039] The digital image is used to display numbers, and the numbers are used to assist in encryption and decryption.

[0040] In this embodiment, a pre-set digital image is used. The number displayed in the digital image can be flexibly set, for example, set to 3. The number is used to assist in encryption and decryption. It is mainly based on the number to transform the image matrix. For example, the columns of the matrix can be moved to the left or right according to the number, and the rows of the matrix can be moved up or down according to the number.

[0041] The double XOR algorithm involves two XOR operations and combines them with numbers to perform translation transformations on the matrix, which can significantly improve security.

[0042] In step S106, the phase distribution of the key image and the codebook image is determined based on the key image and the codebook image.

[0043] In step S108, the phase distribution of the key image and the codebook image is loaded onto the linearly polarized multiplexed metasurface.

[0044] In step S110, the linearly polarized multiplexed metasurface is irradiated with electromagnetic waves of first and second polarization directions, respectively. Utilizing the phase distribution of the key image and the codebook image, the codebook image is loaded onto the first polarization direction, and the key image is loaded onto the second polarization direction, before being transmitted to the receiving end. The first and second polarization directions are perpendicular.

[0045] In this embodiment, the linearly polarized multiplexed metasurface can be irradiated with electromagnetic waves of two mutually perpendicular polarization directions to obtain two complementary interference holographic images, namely a key image and a codebook image.

[0046] The technical solution of this application loads the codebook image onto an electromagnetic wave with a first polarization direction and the key image onto an electromagnetic wave with a second polarization direction. Since the two polarization directions are perpendicular, the mutual interference between the codebook image and the key image during transmission is reduced, which is beneficial to improving the quality of image transmission. Since the codebook image and the key image are based on the original image, the digital image is cleverly utilized, matrix transformation is employed, and a double XOR algorithm is used. Through careful design, the receiving end can restore the original image based on the codebook image and the key image, which significantly improves security.

[0047] In some embodiments, step S104 involves obtaining a key image and a codebook image by using a double XOR algorithm based on the matrix of the original image and the matrix of a pre-defined digital image, including:

[0048] The following principles are used to determine the key image and the codebook image:

[0049] The result of XORing the matrix of the codebook image and the matrix of the key image is equal to the matrix of the digital image.

[0050] Based on the numbers displayed in the digital image, the key matrix is ​​transformed to obtain an updated key image matrix.

[0051] The result of XORing the matrix of the codebook image with the matrix of the updated key image is equal to the matrix of the original image.

[0052] The following uses formula notation, where B represents the matrix of the codebook image and A represents the matrix of the key image. Let Y represent the matrix of the updated key image; let Y represent the matrix of the original image; let 3 represent the matrix of the digital image; the above conditions can be simplified using the following formula:

[0053] ; Shift matrix A cyclically 3 columns to the left to obtain matrix ;

[0054] ;

[0055] .

[0056] In this embodiment, exhaustive search and random trial methods can be used to determine the corresponding key image and codebook image based on the three conditions mentioned above. The solutions for the key image and codebook image may not be unique.

[0057] For example, in one implementation, a preliminary key image can be randomly set first, and then the randomly set key image can be used in the above conditions to verify whether the codebook image can be obtained.

[0058] Specifically, based on the matrix of the initial key image mentioned above, matrix transformations can be performed according to the numbers in the digital image. For example, column shifting or row shifting can be performed to obtain the initial updated key image.

[0059] Based on the initial key image matrix and digital image matrix, an XOR operation is performed to obtain the codebook image matrix;

[0060] The matrix of the original image is XORed with the matrix of the preliminary updated key image to obtain the matrix of the codebook image.

[0061] Verify whether the matrices of the above codebook images are the same. If they are not the same, make adjustments.

[0062] In some embodiments, the dimensions of the metasurface are determined based on the dimensions of the original image;

[0063] Each pixel of the original image corresponds to a size unit in the metasurface.

[0064] In this embodiment, the aforementioned size unit can be If the original image has 100 pixels The dimensions of the metasurface are then... .

[0065] In some embodiments, the phase distribution of the key image and the codebook image is determined based on the key image and the codebook image;

[0066] Based on the phase distribution of the key image, the electromagnetic wave in the first polarization direction is modulated to load the key image onto the electromagnetic wave in the first polarization direction.

[0067] Based on the phase distribution of the codebook image, the electromagnetic wave in the second polarization direction is modulated to load the codebook image onto the electromagnetic wave in the second polarization direction.

[0068] In some embodiments, a hybrid phase distribution is generated based on the phase distribution of the codebook image and the phase distribution of the key image;

[0069] The hybrid phase distribution includes a hybrid-coded pixel array. For any hybrid-coded pixel, the color of the pixel is determined by a combination of the phase coding of the electromagnetic wave in the first polarization direction and the phase coding of the electromagnetic wave in the second polarization direction.

[0070] In this embodiment, based on the combination of the phase encoding of the electromagnetic wave in the first polarization direction and the phase encoding of the electromagnetic wave in the second polarization direction, four combinations are obtained, and each combination corresponds to a color. For example, 00 corresponds to dark blue, 10 corresponds to sky blue, 01 corresponds to green, and 11 corresponds to yellow.

[0071] The above-mentioned mixed phase distribution is loaded onto the polarization multiplexing metasurface, and when irradiated with electromagnetic waves of the first polarization direction, the reflected electromagnetic waves of the first polarization direction will carry key image information.

[0072] When irradiated with electromagnetic waves of the second polarization direction, the reflected electromagnetic waves of the second polarization direction will carry the codebook image information.

[0073] See appendix Figure 2 The diagram shown is a phase distribution diagram; in which,

[0074] Figure 2 (a) is the phase encoding distribution of the letter image "L" in the x-polarization direction of the corresponding metasurface;

[0075] Figure 2 (b) is the phase encoding distribution of the letter image "L" in the y-polarization direction of the corresponding metasurface;

[0076] Figure 2 (c) is the phase encoding distribution of the letter image "O" in the x-polarization direction of the corresponding metasurface;

[0077] Figure 2 (d) is the phase encoding distribution of the letter image "O" in the y-polarization direction of the corresponding metasurface;

[0078] Figure 2 (e) is the phase encoding distribution of the letter image "V" in the x-polarization direction of the corresponding metasurface;

[0079] Figure 2 (f) is the phase encoding distribution of the letter image "V" in the y-polarization direction of the corresponding metasurface;

[0080] Figure 2(g) is the phase encoding distribution map of the letter image "E" in the x-polarization direction of the corresponding metasurface;

[0081] Figure 2 (h) is the phase encoding distribution of the letter image "E" in the y-polarization direction of the corresponding metasurface;

[0082] See appendix Figure 3 The diagram shows a phase distribution of a coding combination; in which,

[0083] Figure 3 (i) represents the phase encoding combination of the letter L in the x and y directions of the corresponding metasurface;

[0084] Figure 3 (j) represents the phase encoding combination of the letter O in the x and y directions of the corresponding metasurface;

[0085] Figure 3 (k) represents the phase encoding combination of the letter V in the x and y directions of the corresponding metasurface;

[0086] Figure 3 (l) represents the phase encoding combination of the letter E in the x and y directions of the corresponding metasurface.

[0087] In each of the phase coding combinations mentioned above, the first digit represents the code for the x-polarization direction, and the second digit represents the code for the y-polarization direction. The x-polarization direction and the y-polarization direction are orthogonal.

[0088] To achieve better imaging results, a 50×50 metasurface array was used. Since the unit period is 12mm, a large 600×600mm metasurface was designed. The target image has 600×600 pixels, with each pixel designed to be 1mm×1mm, thus enabling the generation of a holographic image of the same size as the metasurface on a preset plane. The target image was loaded onto the metasurface phase using a microwave imaging-based GS algorithm. The iterative calculation process was performed in MATLAB software, resulting in the pure phase map shown in the figure above.

[0089] The string consists of four letters, therefore, four metasurfaces are needed in the design to reproduce the target image. The x and y polarization of each metasurface produces a "key" image and a "codebook" image for each letter, respectively.

[0090] The first row of images shows the metasurface phase distribution corresponding to each "key" image, and the second row shows the phase distribution of the "codebook" image. The blue and yellow blocks represent the encoding of the metasurface unit, that is, the encoding during unit design. This encoding enables the loading of images onto the metasurface.

[0091] See appendix Figure 4By linking the unit parameters with the code and using VBA code, the metasurface plane is automatically modeled to obtain a complete metasurface.

[0092] The example metasurface in the figure is a metasurface for transmitting the letter O, composed of 50×50 units. The holographic pattern in the figure is generated by this metasurface under electromagnetic wave illumination on the x-polarized plane. Each unit of the metasurface can be regarded as a point source, and together they generate a holographic pattern on a predetermined plane. The figure shows the unit distribution in the upper left corner of the metasurface, with four types of units arranged in... Figure 3 Phase arrangement in (j).

[0093] The other three metasurface arrays were arranged in the same way. Each complete metasurface was simulated under electromagnetic waves in the x and y polarization planes. The electromagnetic response of the metasurface in the preset plane was calculated using the finite-time integral method to obtain a holographic image.

[0094] The circuit-type phase modulation mechanism is well-suited for the XOR encryption scheme, so a circuit-type cell is still chosen in the cell design. Since it is necessary to control two mutually orthogonal polarization directions simultaneously, vertical metal blocks of the same size as the x-axis metal rod are added to both ends of the metal rod in the y-axis direction. The addition of these metal blocks effectively adds a capacitor in the y-axis direction. Similar to the x-axis direction, changing the length of the y-axis metal rod alters the parameters of the equivalent LC circuit in the y-axis direction, thereby changing the phase delay of the cell.

[0095] See appendix Figure 5 Based on the above approach, this application proposes a metasurface unit for a linearly polarized multiplexed metasurface. This unit has a three-layer structure: a surface layer of metal structure, a middle layer of dielectric, and a bottom layer of metal reflective. The metal structure layer exhibits an axisymmetric structure in both the x and y polarization directions. The metal rods in both polarization directions are identical in size, except for the length of the central metal rod (lx and ly in the figure).

[0096] In some embodiments, the metasurface includes an array of metasurface units; each metasurface unit includes a surface layer, an intermediate layer, and a bottom layer. The surface layer is a metallic structural layer. The intermediate layer is a dielectric layer. The bottom layer is a metallic reflective layer. The surface layer includes an integrally formed cross-shaped body and four extensions.

[0097] The intersecting body is composed of a first long strip metal piece and a second long strip metal piece arranged perpendicularly to each other, and the central axis of the first long strip metal piece and the central axis of the second long strip metal piece are perpendicular to each other and intersect at the midpoint of the two.

[0098] The four extension portions are respectively provided at both ends of the first long strip metal piece and both ends of the second long strip metal piece. Each extension portion is a long strip metal piece, and the central axis of the corresponding metal piece passes perpendicularly through the midpoint of the extension portion. The central axis of the extension portion is set perpendicular to the central axis of the corresponding metal piece.

[0099] The first elongated metal piece, the second elongated metal piece, and the extension have the same thickness, and their bottom surfaces and top surfaces are coplanar.

[0100] The first and second elongated metal parts have different lengths.

[0101] In some embodiments, the first elongated metal piece, the second elongated metal piece, and the extension are all cuboid structures;

[0102] The four extensions are all identical in shape and size;

[0103] The width and thickness of the first and second elongated metal parts are the same.

[0104] The cross-sectional length of the dielectric layer is 12mm and the thickness is 2mm;

[0105] The thickness of the metal structure layer is 0.035 mm;

[0106] The thickness of the bottom layer is the same as the thickness of the metal structure layer;

[0107] The extension is 4mm long and 1mm wide;

[0108] The widths of the first and second elongated metal parts are 2 mm.

[0109] The length lx of the first elongated metal piece is 4.6 mm, and the length ly of the second elongated metal piece is 5.6 mm.

[0110] In some embodiments, the operating frequency of the metasurface unit is 8 Hz.

[0111] Electromagnetic simulation software was used to model the element, and the electromagnetic response parameters in the x and y directions were calculated using the finite-time integral method. Annealed copper was used as the element metal, and FR4 material (dielectric constant: 4.6; loss tangent: 0.016) was used as the dielectric. A frequency domain solver was used. The reflection amplitude and phase delay of the element were calculated in the 2-10 GHz frequency range. After continuous optimization and adjustment, the optimal element response was finally obtained at 8 GHz.

[0112] See appendix Figure 6Two independent metal rod length parameters are also obtained in the x and y directions, and these are combined to form four units. Each unit is encoded separately in the two orthogonal directions as a 1-bit characteristic. To increase the information carried by each unit, they are combined to form a 2-bit unit.

[0113] In order to achieve polarization reuse, the metasurface unit must not affect each other under two orthogonal polarizations and must be able to generate sufficient phase delay and reflection amplitude to achieve the preset imaging effect under each polarization.

[0114] See appendix Figure 7 The response results shown are obtained by simulating the above four units under x and y polarization respectively and calculating their amplitude and phase responses.

[0115] As shown in the figure, 7(a) and 7(b) illustrate the amplitude and phase responses of the four units under x-polarization, while 7(c) and 7(d) illustrate the responses under y-polarization. The four units are represented by curves of different colors; the first number indicates the unit code under x-polarization, and the second number indicates the unit code under y-polarization. It can be observed from the figure that under single-polarization electromagnetic wave illumination, the size change in the other cross-polarization direction has little effect on the amplitude and phase responses of these four units. Units of the same size in the same polarization direction almost overlap in their response curves under this polarization. Units of different sizes exhibit almost identical reflection amplitudes at 8 GHz, all reaching 0.9, suitable for high-resolution holographic imaging. Their phase responses at 8 GHz all satisfy a 180° phase difference, and are considered 1-bit units in a single polarization direction. Therefore, the four units form 2-bit units in two polarization directions, and each polarization direction can independently generate the desired response without affecting the others.

[0116] The design of the unit combines the principles of circuit-type phase modulation and cross-polarization co-modulation to obtain polarization-multiplexed metasurface units, and each unit is encoded. The encoding principle is distinguished by the phase variables of the unit; 0 and 1 only represent the phase difference, not the absolute phase value. This unit is a phase-coded unit, and there is no need to consider the amplitude variable. This unit encoding facilitates the subsequent arrangement and addressing of the metasurface holographic array.

[0117] This application proposes a linearly polarized multiplexed metasurface capable of independently controlling two orthogonally linearly polarized electromagnetic waves. Information is encrypted into the electromagnetic wave polarization, allowing the same metasurface to generate two different encrypted images, thus achieving metasurface polarization multiplexing. Relying on an XOR double-verification encryption algorithm, the polarization-multiplexed metasurface encryption maintains strong security. Due to the polarization multiplexing of the metasurface, the cost is reduced, increasing its applicability. The polarization-multiplexed metasurface calculates independent phase distributions on the two orthogonal polarizations using an improved microwave band GS algorithm, and reproduces the target pattern on the target's imaging plane. The target pattern is provided by an XOR encryption algorithm, and the two orthogonal holographic images of the same metasurface are used to transmit encrypted information. This application's technical solution comprehensively designs a string of encrypted information reproduction, extends the XOR encryption algorithm, and provides a new approach for metasurface encryption schemes.

[0118] See appendix Figure 8 An image decryption method based on linearly polarized multiplexed metasurfaces includes:

[0119] In step S902, electromagnetic waves with the first polarization direction and the second polarization direction are received based on the linearly polarized multiplexed metasurface.

[0120] The electromagnetic wave in the first polarization direction carries key image information, and the electromagnetic wave in the second polarization direction carries codebook image information.

[0121] In this embodiment, the receiver receives electromagnetic waves with a first polarization direction and a second polarization direction transmitted by the transmitter. The receiver has a linearly polarized multiplexing metasurface, and the linearly polarized multiplexing metasurface of the receiver and the linearly polarized multiplexing metasurface of the transmitter have mutually matched encoding rules. In some embodiments, the linearly polarized multiplexing metasurface of the receiver and the linearly polarized multiplexing metasurface of the transmitter may have the same structural shape and the same phase distribution.

[0122] In step S904, a double XOR decryption algorithm is used to obtain the original image based on the key image and the codebook image.

[0123] Wherein, the first polarization direction is perpendicular to the second polarization direction.

[0124] In this embodiment, the decryption algorithm also uses a double XOR operation to decrypt the key image and the codebook image to obtain the original image.

[0125] In some embodiments, step S904, employing a double XOR decryption algorithm to obtain the original image based on the key image and the codebook image, may further include the following steps:

[0126] Perform an XOR operation on the matrix of the key image and the matrix of the codebook image to obtain the matrix of the digital image;

[0127] Based on the numbers displayed in the digital image, a matrix transformation operation is performed on the matrix of the key image to obtain an updated key image.

[0128] The transformation operation can perform column-wise or row-wise translation. For example, if the number is 3, the key image matrix will be shifted 3 columns to the left.

[0129] The updated key image is XORed with the codebook image to obtain the original image.

[0130] In this embodiment, since the key image and codebook image sent are carefully designed to conform to the sending end's settings, these principles enable the key image and codebook image to implement the steps of the method described above. For example, performing an XOR operation between the updated key image and the codebook image to obtain the original image is based on the third condition in the principle: the result of an XOR operation between the matrix of the codebook image and the matrix of the updated key image is equal to the matrix of the original image. Because the XOR operation is commutative, according to the third condition, performing an XOR operation between the updated key image and the codebook image to obtain the original image is possible.

[0131] The following example illustrates the encryption and decryption process by showing the word "LOVE" sent by the sender and received by the receiver.

[0132] See appendix Figure 9 The blue box on the left shows a series of target patterns, generated directly in space by metasurface holographic imaging. The red box on the right shows the decrypted pattern obtained from the target patterns on the left using a double XOR algorithm. The digital images obtained from the first layer of decryption represent left-shift matrix operations. The intensity distribution of the preset holographic pattern is obtained by the XOR encryption algorithm, which is derived by reverse engineering from the target encrypted pattern and does not carry any decryption pattern information.

[0133] The first column of images within the blue frame contains the holographic images of the "key" that each metasurface needs to generate, and the second column contains the holographic images of the "codebook" that each metasurface needs to generate.

[0134] The first column of images within the red box on the right are all digital images, obtained by directly XORing the "key" image and the "codebook" image, representing a matrix operation.

[0135] For example, the image in the first row and first column within the red box on the right displays "2", indicating that the column of the matrix of the "key" holographic image (first row and first column within the blue box) has been shifted two columns to the left. The image in the second row and first column within the red box on the right displays "4", indicating that the column of the matrix of the "key" holographic image (second row and first column within the blue box) has been shifted four columns to the left.

[0136] The second column of images within the red box is the final decrypted image, which is the original image. It is obtained by XORing the "key" image (after matrix operation) with the original "codebook" image. These images, when arranged together, can form the string "LOVE", which expresses a specific meaning, indicating successful decryption.

[0137] As can be seen from the image, the final recovered pattern contained some redundant pixels during the design process. This is because the image has too few pixels (5×5 pixels, matrix operands 1-4). This XOR encryption algorithm, if not converging, would generate noise with the same number of columns as the matrix operands. Therefore, to ensure algorithm convergence, redundant pixels were added to the final decryption pattern design. However, these redundant pixels do not affect the meaning of the pattern; each letter in "LOVE" is still recognizable.

[0138] See appendix Figure 10 There are a total of 16 holographic images. The first two rows of holographic images are the holographic images recovered by the receiver, the third row is the digital image decrypted at the first layer, and the fourth row is the finally decrypted image, which is the original image.

[0139] To ensure clarity, each holographic image is divided into 5×5 matrix blocks. Each focal point is located at the center of the matrix block and has a high intensity value, representing the intensity value of each matrix block. After calculating the intensity value of each matrix block, it is binarized. Matrix blocks exceeding a threshold are considered as 1, and matrix blocks below the threshold are considered as 0.

[0140] in, Figure 10 (a) is the key image of the letter L;

[0141] Figure 10 (b) is a codebook image of the letter L;

[0142] Figure 10 (c) is a digital image of the letter L;

[0143] Figure 10 (d) is the original image of the letter L, which is the decrypted image;

[0144] Figure 10 (e) is the key image of the letter O;

[0145] Figure 10 (f) is a codebook image of the letter O;

[0146] Figure 10 (g) is a digital image of the letter O;

[0147] Figure 10 (h) is the original image of the letter O, which is the decrypted image;

[0148] Figure 10 (i) is the key image of the letter V;

[0149] Figure 10 (j) is a codebook image of the letter V;

[0150] Figure 10 (k) is a digital image of the letter V;

[0151] Figure 10 (l) is the original image of the letter V, which is the decrypted image;

[0152] Figure 10 (m) is the key image of the letter E;

[0153] Figure 10 (n) is a codebook image of the letter E;

[0154] Figure 10 (o) is a digital image of the letter E;

[0155] Figure 10 (p) is the original image of the letter E, which is the decrypted image.

[0156] Each letter corresponds to a supersurface, and there are four supersurfaces in total.

[0157] For any of the above letters, an XOR operation is performed on the key image and the codebook image to obtain a numerical image displaying the specific Arabic numeral. The Arabic numeral represents the matrix shift performed to update the key image; the shift can be a cyclic left shift. After the key image is updated, an XOR operation is performed on the updated key image and the codebook image matrix to obtain the original image, as shown below. Figure 10 (d) Figure 10 (h) Figure 10 (l) and Figure 10 As shown in (p), the letters in the image are clearly visible and, when combined, form the string "LOVE," representing the meaning of "love."

[0158] The repetition of "LOVE" signifies the completion of the encryption and decryption process, and also indicates the effectiveness of the metasurface encryption and decryption scheme proposed in this application. This application utilizes the circuit-type phase principle to design polarization multiplexing units, enabling them to independently control electromagnetic waves in two cross-polarization directions. Arranging these units according to the target phase distribution allows for the independent generation of different holographic images under electromagnetic wave illumination from the two polarization planes, increasing the information carrying capacity of the metasurface. Based on this, an XOR double encryption algorithm is used to link the holographic images under the two polarizations, requiring them to participate in decryption to obtain the final encrypted information, thus increasing system security. Simultaneously, the metasurface itself possesses the capacity to store large amounts of information. Extending this scheme to the optical band is expected to generate ultra-high resolution encryption patterns. This scheme has significant application value in fields such as optical encryption and space communication.

[0159] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

Claims

1. An image encryption method based on linear polarization multiplexing metasurface, characterized in that, include: Obtain the original image; Based on the matrix of the original image and the matrix of the pre-set digital image, a double XOR algorithm is used to obtain the key image and the codebook image; The digital image is used to display numbers, and the numbers are used to assist in encryption and decryption. The phase distribution of the key image and the codebook image is determined based on the key image and the codebook image; The phase distributions of the key image and the codebook image are loaded onto a linearly polarized multiplexed metasurface; The linearly polarized multiplexed metasurface is irradiated with electromagnetic waves of the first polarization direction and the second polarization direction, respectively. Utilizing the phase distribution of the key image and the codebook image, the codebook image is loaded onto the first polarization direction, and the key image is loaded onto the second polarization direction, and then sent to the receiving end. The first polarization direction is perpendicular to the second polarization direction.

2. The image encryption method based on line polarization multiplexed metasurface according to claim 1, characterized in that, Based on the matrix of the original image and the matrix of the pre-defined digital image, a double XOR algorithm is used to obtain the key image and the codebook image, including: The following principles are used to determine the key image and the codebook image: The result of XORing the matrix of the codebook image and the matrix of the key image is equal to the matrix of the digital image; Based on the numbers displayed in the digital image, the key matrix is ​​transformed to obtain an updated key image matrix; The result of XORing the matrix of the codebook image with the matrix of the updated key image is equal to the matrix of the original image.

3. The image encryption method based on linearly polarized multiplexed metasurfaces according to claim 1, characterized in that, The dimensions of the metasurface are determined based on the dimensions of the original image; Each pixel of the original image corresponds to a size unit in the metasurface.

4. The image encryption method based on line polarization multiplexed metasurface according to claim 1, characterized in that, The metasurface includes a metasurface unit array; Each metasurface unit consists of: a surface layer, an intermediate layer, and a bottom layer; The surface layer is a metal structure layer; The intermediate layer is a dielectric layer; The bottom layer is a metal reflective layer; The surface layer includes: an integrally formed cross body and four extensions; The intersecting body is composed of a first long strip metal piece and a second long strip metal piece arranged perpendicularly to each other, and the central axis of the first long strip metal piece and the central axis of the second long strip metal piece are perpendicular to each other and intersect at the midpoint of the two. The four extension portions are respectively provided at both ends of the first long strip metal piece and both ends of the second long strip metal piece. Each extension portion is a long strip metal piece, and the central axis of the corresponding metal piece passes perpendicularly through the midpoint of the extension portion. The central axis of the extension portion is set perpendicular to the central axis of the corresponding metal piece. The first elongated metal piece, the second elongated metal piece, and the extension have the same thickness, and their bottom surfaces and top surfaces are coplanar. The first and second elongated metal parts have different lengths.

5. The image encryption method based on linearly polarized multiplexed metasurfaces according to claim 4, characterized in that, The first elongated metal piece, the second elongated metal piece, and the extension are all cuboid structures; The four extensions are all identical in shape and size; The width and thickness of the first and second elongated metal parts are the same.

6. The image encryption method based on linearly polarized multiplexed metasurfaces according to claim 1, characterized in that, The operating frequency of the metasurface unit is 8 Hz.

7. The image encryption method based on linearly polarized multiplexed metasurfaces according to claim 5, characterized in that, The cross-sectional length of the dielectric layer is 12mm and the thickness is 2mm; The thickness of the metal structure layer is 0.035 mm; The thickness of the bottom layer is the same as the thickness of the metal structure layer; The extension is 4mm long and 1mm wide; The widths of the first and second elongated metal parts are 2 mm. The length of the first elongated metal piece is 4.6 mm, and the length of the second elongated metal piece is 5.6 mm.

8. An image decryption method based on a linearly polarized multiplexed metasurface, characterized in that, include: Electromagnetic waves with first and second polarization directions are received based on a linearly polarized multiplexed metasurface. The electromagnetic wave in the first polarization direction carries the key image, and the electromagnetic wave in the second polarization direction carries the codebook image. The original image is obtained by using a double XOR decryption algorithm based on the key image and the codebook image; Wherein, the first polarization direction is perpendicular to the second polarization direction.

9. The image decryption method based on linearly polarized multiplexed metasurfaces according to claim 8, characterized in that, Using a double XOR decryption algorithm, the original image is obtained based on the key image and the codebook image, including: Perform an XOR operation on the matrix of the key image and the matrix of the codebook image to obtain the matrix of the digital image; Based on the numbers displayed in the digital image, the matrix of the key image is transformed to obtain an updated key image; The updated key image is XORed with the codebook image to obtain the original image.

10. An image encryption and decryption system based on a linearly polarized multiplexed metasurface, characterized in that, Includes the sending end and the receiving end; The transmitting end is used to employ the steps of the image encryption method based on linearly polarized multiplexed metasurfaces as described in any one of claims 1 to 7; The receiving end is used to employ the steps of the image decryption method based on linearly polarized multiplexed metasurfaces as described in any one of claims 8 to 9.

Images