Optical encryption steganography method and system based on multi-channel metasurface

Abstract

The invention provides an optical encryption steganography method and system based on a multi-channel metasurface, and relates to the technical field of metasurface optical encryption, and the method mainly comprises the steps: constructing a dual-structure non-spatial multiplexing three-channel metasurface according to the material characteristics of a dual-wavelength metasurface; a first super-composition image used for transmitting secret information extraction and recovery parameters, and a second super-composition image and a third super-composition image which are embedded with secret information by using a steganography algorithm based on run length coding are coded into the double-structure non-spatial multiplexing three-channel metasurface for optical encryption; and decrypting them requires different levels of optical keys. According to the invention, the risk that information is easy to be cracked by exhaustion due to a single key level can be reduced, and the optical encryption information is prevented from being directly observed by using a multi-carrier information steganography method.

Description

Technical Field

[0001] The present invention belongs to the field of super-surface optical encryption technology, and in particular, relates to an optical encryption steganography method and system based on a multi-channel super-surface. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Nowadays, information security is important in all aspects of life. In order to prevent information from being stolen or tampered with, various information encryption technologies have emerged. Among them, optical encryption converts plaintext information into complex and difficult-to-interpret optical signals by utilizing light interference, diffraction, and imaging, providing an efficient and reliable solution for the encryption and processing of high-security information.

[0004] Metasurface is a kind of artificially designed two-dimensional planar optical metamaterial, which is usually composed of nanostructures with customized shapes and subwavelength characteristic sizes, namely meta-atomic arrays. Due to its unprecedented ability to control local light fields at subwavelength scales, metasurfaces have been successfully applied to realize a variety of compact and miniaturized planar functional devices, such as holographic display, polarization conversion, light focusing, and vortex beams. At present, metasurfaces have been widely used to explore new types of optical encryption by manipulating different photon degrees of freedom such as polarization, amplitude, phase, and orbital angular momentum. In particular, the emergence of various multiplexed metasurfaces makes it possible to encode ultra-high-resolution multi-channel image information in the same metasurface. Among them, the image information in each channel needs to be observed under specific optical illumination conditions, namely optical keys, so it can be regarded as optical encryption of multi-channel image information.

[0005] However, most of the current multi-channel optical encryption metasurfaces have a single optical key level. When the key of one channel is known, the keys of other channels are easily cracked due to the same form, which seriously threatens the security of information. In addition, most of the currently proposed optical encryption metasurfaces encrypt plaintext information in the form of image display. The encrypted information is encoded in each channel of the metasurface in the form of image display, so that the secret information can be directly observed, resulting in the risk of information being easily stolen. The existing advanced information encryption method that combines metasurfaces with cryptographic encryption algorithms may cause suspicion of spies due to the presence of pseudo-random ciphertext information in multiple channels, making the information easy to be reviewed and cracked, which has certain disadvantages. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides an optical encryption steganography method and system based on a multi-channel metasurface, which can enable the multi-channel metasurface optical keys to have two levels, high and low, effectively reducing the risk of information being easily cracked due to the single key level; and integrating multi-carrier information steganography into the field of metasurface optical encryption, effectively preventing the optically encrypted information from being directly observed.

[0007] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: The first aspect of the present invention provides an optical encryption steganography method based on a multi-channel metasurface.

[0008] An optical encryption steganography method based on a multi-channel metasurface, comprising: According to the material properties of the dual-wavelength metasurface, a dual-structure non-spatial multiplexing three-channel metasurface is constructed; Acquire secret information, perform scrambling preprocessing to obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first hyperstructured image; Based on the run-length coding steganographic algorithm, two carrier images are selected. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images, and the images are reconstructed to obtain the second and third super-images embedded with the secret information. The first meta-image, the second meta-image and the third meta-image are respectively encoded into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

[0009] The second aspect of the present invention provides an optical encryption steganography system based on a multi-channel metasurface.

[0010] An optical encryption steganography system based on a multi-channel metasurface, comprising: The channel construction module is configured to: construct a dual-structure non-spatial multiplexed three-channel metasurface according to the material properties of the dual-wavelength metasurface; The hyperstructured image acquisition module is configured to: acquire secret information, perform scrambling preprocessing, obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first hyperstructured image; Based on the run-length coding steganographic algorithm, two carrier images are selected. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images, and the images are reconstructed to obtain the second and third super-images embedded with the secret information. The optical encryption module is configured to respectively encode the first meta-image, the second meta-image and the third meta-image into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

[0011] A third aspect of the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0012] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which executes the steps of the above method when executed by a processor.

[0013] One or more of the above technical solutions have the following beneficial effects: The present invention provides an optical encryption steganography method and system based on a multi-channel metasurface. Different from most previous optical encryption works that utilize the different responses of metasurfaces to different optical lighting conditions, the present invention introduces image-based steganography into the field of optical encryption based on the ultra-high resolution image display advantage of metasurfaces, utilizes multiple images to disperse and carry secret information, and then encodes the multiple images carrying secret information into optical images in the multi-channel metasurface for encrypted transmission.

[0014] In the present invention, by adjusting different wavelength and polarization key combinations for two different sizes of nanostructures of the multi-channel metasurface, a dual-structure non-spatial multiplexed three-channel metasurface is constructed, thereby realizing ultra-high resolution encrypted display of three binary images at two wavelengths, so that the multi-channel metasurface optical keys exist in two levels, which effectively reduces the risk of information being easily cracked due to a single key level.

[0015] In the present invention, multi-carrier information steganography is integrated into the field of metasurface optical encryption, giving full play to the advantages of metasurface in ultra-high resolution image display and multi-channel joint regulation, and using full-channel encrypted optical images to jointly hide secret information to protect the secret information from direct observation and leakage.

[0016] In the present invention, when extracting secret information, it is necessary to use optical keys to obtain the encrypted image information in all channels, and then combine the encrypted optical images in all channels to extract and decode the secret information, giving full play to the advantages of the metasurface in multi-channel joint regulation.

[0017] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0019] Figure 1 This is a conceptual diagram of an optical encryption steganography method based on a multi-channel metasurface according to Embodiment 1 of the present invention; Figure 2 Schematic diagram of the unit cell PT and PR structure of the super surface nanostructure in Example 1 of the present invention; Figure 3 It is a schematic diagram of simulated transmittance of polarized light incident along the L axis and W axis of the PT structure according to the first embodiment of the present invention; Figure 4 It is a schematic diagram of simulated transmittance of polarized light incident along the L axis and W axis of the PR structure according to the first embodiment of the present invention; Figure 5 This is a schematic diagram of simulated transmittance of the first channel and the second channel of the PT structure at different orientation angles at a wavelength of 633 nm according to the first embodiment of the present invention; Figure 6 This is a schematic diagram of simulated transmittance of the first channel and the second channel of the PR structure at different orientation angles at a wavelength of 633 nm according to the first embodiment of the present invention; Figure 7 This is a schematic diagram of theoretical transmittance corresponding to different structural orientation angles in the first channel and the second channel of Example 1 of the present invention; Figure 8 This is a schematic diagram of the variation of the total transmittance of the two structures at different orientation angles at a wavelength of 750 nm according to Example 1 of the present invention; Fig. 9 This is a schematic diagram of recording eight different binary codes into two different nanorod structure orientation angles according to the first embodiment of the present invention; Fig.10 This is a schematic diagram of a process of performing run-length encoding on a carrier image and preprocessing secret information according to an embodiment of the present invention; Fig.11 This is a schematic diagram of a process of embedding secret information into a carrier image in Embodiment 1 of the present invention; Fig.12 The first super-image retrieved by using a higher-level optical key according to the first embodiment of the present invention; Fig.13 The second super-image retrieved by using a higher-level optical key according to the first embodiment of the present invention; Fig.14 The third super-image retrieved by using the optical key of a lower level in the first embodiment of the present invention; Fig.15 Schematic diagram of the process of extracting and recovering secret information according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0020] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0021] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0022] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0023] Embodiment 1 This embodiment discloses an optical encryption steganography method based on a multi-channel metasurface. Figure 1 As shown, the following steps are included: Step S1: construct a dual-structure non-spatial multiplexing three-channel metasurface based on the material properties of the dual-wavelength metasurface.

[0024] Step S1-1, forming a dual-wavelength metasurface by using hydrogenated amorphous silicon (a-Si:H) nanorods of two different sizes on a glass (SiO2) substrate.

[0025] In this embodiment, for the convenience of representation, the two designed nanocolumns are named PT and PR respectively. The first letter P indicates that the two nanobrick structures act as polarizers at the wavelength λ1, and the second letters T and R represent the high transmittance and low transmittance of the structure at the wavelength λ2, respectively. Among them, at the wavelength λ2, the PT structure exhibits polarization-independent efficient transmission, and the PR structure exhibits polarization-independent efficient reflection (corresponding to low transmittance). "Polarization-independent" means that no matter what the polarization of the incident light is, one structure can efficiently transmit the incident light, while the other structure can efficiently reflect the incident light.

[0026] like Figure 2 As shown, two rectangular unit cell structures with PT and PR functions are shown, and their geometric parameters are: PT length is L1 = 60nm, width is W1 = 130nm, and height is H1 = 220nm; PR length is L2 = 140nm, width is W2 = 225nm, height is H2 = 220nm, and the period of the unit cell is P = 320nm.

[0027] like Figure 3 and Figure 4As shown in the figure, the transmission spectra of PT and PR under linear polarized light incident along the L axis and W axis are shown respectively. The results show that at wavelength λ1, the transmittance of the polarization axis and the non-polarization axis of the two structures of PT and PR differ by about 87% and 75%, respectively; at wavelength λ2, the transmittance of the two axes of the PT structure is above 94%, while the transmittance of the two axes of the PR structure is below 2%, which meets the requirements. In addition, the two structures still have the expected characteristics near the designed working wavelength, indicating that the structural function has a certain robustness to the change of wavelength.

[0028] Step S1-2: selecting a working wavelength λ1 and a working wavelength λ2 based on the material properties of the dual-wavelength metasurface.

[0029] In this embodiment, considering the high refractive index and low absorption of a-Si:H material in the near-infrared band, two working wavelengths of λ1=633nm and λ2=750nm are selected.

[0030] Step S1-3, at the working wavelength λ1, the two nanorods of different sizes are used as nanopolarizers, a polarizer and an analyzer are placed in front and behind them respectively, and two non-orthogonal polarization light paths are constructed by adjusting the orientation angle of the nanorods and the directions of the polarizer and the analyzer, which are defined as the first channel and the second channel respectively; The intensity of the output light can be controlled by fixing the orientation angle α of the structure. By setting different combinations of polarization direction θ1 and analysis direction θ2, two non-orthogonal polarization light paths are constructed, thereby realizing a dual-channel design in which the transmitted light intensity depends on the structural orientation angle at wavelength λ1.

[0031] When the nanostructure is used as a nanopolarizer, the intensity of the output light can be controlled by fixing the orientation angle of the structure, specifically: It is known that the Jones matrix M of a nanorod with an orientation angle α in a plane is α It can be expressed as:

[0032] Where R(α) is the rotation matrix, M0 represents the Jones matrix of an ideal nanorod that does not produce cross-polarization components, and A and B are the complex transmission (or reflection) coefficients of polarized light along the x-axis and y-axis, respectively.

[0033] Since the Jones matrix has a close connection between the input field and the output field, this embodiment uses a polarizer and an analyzer to control the polarization direction of the incident light and the transmitted light. Therefore, when linearly polarized light (Jones vector J0) with a polarization angle of θ1 is incident, the transmitted light passes through the analyzer, and the Jones vector J1 of the final output light can be expressed as:

[0034] Where θ1 and θ2 are the transmission axis directions of the polarizer and analyzer, respectively. is the Jones matrix of the polarizer. When the intensity of the incident linear polarized light is I0, after passing through the polarizer, the calculation formula for the intensity of the outgoing light is:

[0035] When the nanostructure is regarded as an ideal polarizer (let A = 1, B = 0), the formula for the outgoing light intensity can be simplified to:

[0036] According to the above formula, by carefully selecting different combinations of the polarization direction θ1 of the polarizer and the transmission direction θ2 of the analyzer, a dual-channel design in which the transmitted light intensity depends on the structural orientation angle can be realized. As a verification example, the polarizer-analyzer combination selected here is: first channel: θ1= 30° and θ2= 75°; second channel: θ1= -15° and θ2= 30°.

[0037] In this embodiment, based on Malus's law, the transmittance of the two structures of PT and PR under dual channels is simulated and studied at wavelength λ1. The results are as follows: Figure 5 and Figure 6 As shown, the curve in the figure shows the changing trend of the structural transmittance with different orientation angles.

[0038] In order to intuitively compare the difference between the two structures as nanopolarizers and theoretical polarizers in dual-channel design, Figure 7 The theoretical transmittance of the dual channel at different orientation angles of the structure is shown. In the figure, the gray dashed lines mark the four selected orientation directions and their corresponding two-bit binary intensity coding states under the dual channel.

[0039] like Figure 7 As shown, the codes 00-11 are determined according to the light intensity. Figure 7 The distribution curves of the transmitted light intensity under these two channels with the structural orientation angle are shown. It can be seen that the simulation curves of the two selected structures are consistent with the change trend of the theoretical curves.

[0040] We selected four fixed structural orientation angles for each nanocolumn: 30°, 75°, 120°, and 165°, and encoded the light intensity of the two channels at these four orientation angles. The high light intensity is encoded as 1, and the low light intensity is encoded as 0. We also recorded four different binary encoding states of "11", "10", "00" and "01" in two different channels at this wavelength to achieve the encoding of two binary images of the polarizer channel. Experiments have shown that at the four selected angles, the dual-channel transmittance of the two structures reaches more than 72% of the theoretical transmittance.

[0041] Step S1-4: constructing a third channel at the working wavelength λ2 according to the different transmission light intensities of the two nanorods of different sizes.

[0042] Since the transmitted light intensity of the two structures is only related to the wavelength and has nothing to do with the incident polarization state and the structural orientation angle, an additional single independent channel can be designed at this wavelength.

[0043] In this embodiment, by encoding the PT structure as 1 and the PR structure as 0, an image encoding channel completely independent of the first two channels is designed at wavelength λ2.

[0044] At wavelength λ2, at the four selected orientation angles (30°, 75°, 120°, 165°), the light intensity of the PT structure is high, so it is encoded as 1 at these four angles; while the light intensity of the PR structure is low, so it is encoded as 0 at these four angles. Therefore, at wavelength λ2, the PT structure is encoded as 1 and the PR structure is encoded as 0.

[0045] like Figure 8 As shown in the figure, the total transmittance distribution of PT and PR at different orientation angles at wavelength λ2 is shown. It can be seen that with the change of orientation angle, the total transmittance of the PT structure remains stable close to 1, while the total transmittance of the PR structure is stable at around 0. Therefore, it is verified that at the working wavelength λ1, the encoding of channel 1 and channel 2 is related to the orientation angle of the structure, and has nothing to do with the size of the structure. At the working wavelength λ2, the total transmittance of the two structures is independent of the incident polarization state and the orientation angle of the structure, and is related to the size of the structure.

[0046] Since the metasurface in the present invention is a multi-channel metasurface based on a dual structure, the selection of the polarizer structure of the first channel and the second channel will determine the specific size of the nanopillars (PT or PR) to be used according to the coding in the third channel. Fig. 9 The corresponding relationship between the nanopillar structure array and the light intensity coding distribution of the three channels is shown. It can be seen that each nanopillar participates in the information recording of the three images. The three binary images after optical encryption are composed of 8 binary codes from 000 to 111. The first two bits of the three-bit code (channel 1 and channel 2) are distinguished by the structural orientation angle, and the third bit (channel 3) is distinguished by the structural size (PT or PR).

[0047] According to the structure and design principle selected above, it is possible to encode three images into a single-layer metasurface, providing an optical encryption barrier for the meta-image that transmits secret information extraction and recovery parameters and the meta-image that embeds secret information.

[0048] Different key combinations such as wavelength and polarization are adjusted by two nanostructures of different sizes to construct different levels of optical keys. This is very different from the previous design of three-channel metasurface encryption display with joint regulation of wavelength and polarization state, and lays the foundation for the design of high and low level optical keys.

[0049] Step S2, obtaining secret information, performing scrambling preprocessing to obtain scrambled secret information, generating a QR code using parameters extracted and recovered from the secret information, and obtaining a first hyperimage; In this embodiment, a binary image of 14×14 pixels is the final hidden secret information, and the displayed content is META.

[0050] Since the secret information has continuous identical pixels, in order to avoid regularity and further increase the security of the information, such as Fig.10 As shown, a logistic map is used to generate an iterative sequence with non-periodic and non-convergent properties to scramble the secret information and obtain the scrambled secret information.

[0051] The expression of scrambling preprocessing is:

[0052] Among them, x n is the state value of the nth iteration , x n+1 is x n The next state value of μ is the control parameter (μ (3.56,4]). Since the domain of the iterative sequence is between [0,1], in order to perform XOR operation with the secret information, the threshold is defined as the initial value x0 of the logistic map to construct a 14×14 binary matrix.

[0053] The initial value x0 of the logistic map is used as a string "0.4214" that transmits the secret information extraction and recovery parameters to generate a QR code and obtain the first hyperstructure image; Among them, 4 represents the value of μ in the mapping formula; 2 represents the hint information of the embedding position; 14 represents the pixel size of the secret information; the overall value of 0.4214 represents the initial value x0 of the logistic mapping, with a domain between 0 and 1, which is used to transmit parameter information about the extraction and recovery of secret information.

[0054] Step S3, based on the run-length coding steganographic algorithm, two carrier images are selected, and according to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequences of the two carrier images, and the images are reconstructed to obtain the second super-image and the third super-image embedded with the secret information.

[0055] Run-length encoding (RLE) is considered as a popular compression technique. In RLE, when characters in a string are repeated consecutively, they are replaced by the number of times they occur, which is called the run-length value.

[0056] In this embodiment, the carrier image is a binary image. Since the binary image contains many consecutive identical black and white pixels, they can also be run-length encoded. The specific steps are as follows: Step S3-1, select two binary carrier images of 50×50 pixels.

[0057] like Fig.13 , 14 As shown, carrier image 1 is a cartoon animal, and carrier image 2 is a cartoon girl, and their pixels are run-length encoded respectively.

[0058] Step S3-2: The carrier image 1 can be regarded as a 50×50 matrix, in which white pixels are represented as 1 and black pixels are represented as 0, so it can be scanned column by column to convert its dimension into a continuous 01 sequence.

[0059] Step S3-3, perform run-length encoding on the obtained continuous 01 sequence, and replace the continuous black and white pixels with the number of times they appear; after encoding, all the run-length values ​​constitute a run-length sequence and are named L1, and its length is defined as Length (L1).

[0060] In this embodiment, based on the carrier image 1 we selected, the first run length value of the sequence is 215, which is represented by 215 consecutive 1s, that is, 215 consecutive white pixels.

[0061] Step S3-4: Similarly, the sequence formed by the carrier image 2 after run-length encoding is named L2, and its length is Length (L2).

[0062] Since the carrier image is a binary image, any information to be hidden needs to be converted into a binary sequence if it is to be embedded in it.

[0063] Step S3-5: Scan the scrambled secret information obtained in step S2 column by column to obtain a 01 sequence (Pixel) to be embedded.

[0064] Step S3-6: embed the information in the 01 sequence to be embedded into the running program sequences L1 and L2 in a dispersed manner bit by bit, so as to obtain a running program sequence after the information is embedded.

[0065] like Fig.11As shown, when embedding, first detect the run length value (black pixel run) corresponding to the same even position in L1 and L2. When the embedded information bit is 0, modify the larger value of the two (minus 1) to make them have the same parity; when the information bit is 1, modify the larger value of the two to make them different in parity (if the two run length values ​​are the same at this time, the sequence L1 is modified by default here). When the position embedded in the run sequence exceeds the length of L1, this part of the remaining information will only be embedded in L2. At this time, when the information bit is 0, the run length value of the corresponding position in L2 is modified (minus 1) to an even number; otherwise, it is modified to an odd number. In addition, when the parity and the value to be embedded meet the rules, no modification is made.

[0066] In this embodiment, when a run length value is modified, the last bit of the same continuous binary number when it is not encoded is modified, that is, it changes from 0 to 1, and the pixel of the corresponding carrier image changes from black to white. According to the above rules, the secret information is hidden in two run sequences. The run sequences after embedding the information are named L # 1 and L # 2.

[0067] Step S3-7: the game program sequence L after the embedded information # 1 and L # 2 respectively perform the inverse process of run-length encoding, recover the continuous black and white pixels through decoding the run-length value in the sequence, and then reconstruct the two images embedded with secret information to obtain the second super-image and the third super-image.

[0068] Step S4: respectively encode the first meta-image, the second meta-image and the third meta-image into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

[0069] In this embodiment, the three images of the QR code, the reconstructed cartoon animal and the reconstructed cartoon girl are named as the first super-structured image, the second super-structured image and the third super-structured image respectively.

[0070] Since all three images are binary images, that is, black and white pixel images (black pixels are 0; white pixels are 1). We have previously implemented three-channel encoding at two wavelengths, that is, 000-111. Here we define the first bit of the three-bit encoding to represent the first channel, the second bit to represent the second channel, and the third bit to represent the third channel. Now we need to encode these three binary images into three channels in units of pixels.

[0071] For example, at the same pixel position of the three images in the three channels, the pixels are all black pixels (ie 0), so the code of the three channels at this pixel position is 000, so you need to select the structural rotation angle (120°) of 00 coding (channel 1 and channel 2), and the structural type (PR) of 0 (channel 3); if the three images in the three channels are encoded as 101 at the same pixel position (ie white-black-white: channel 1 is white, channel 2 is black, and channel 3 is white), you need to select the structural rotation angle (75°) of 10 coding (channel 1 and channel 2), and the structural type (PT) of 1 (channel 3); the other codes are similar.

[0072] In this embodiment, in order to verify the feasibility of the proposed optical encryption steganography method based on multi-channel metasurface, we constructed the corresponding single-layer metasurface structure array by carefully selecting specific nanopillars and setting their orientation angles.

[0073] Specifically, three images of the same size (50 × 50 pixels) were recorded simultaneously to 64 × 64 μm 2 In the metasurface sample, each pixel corresponds to a 4×4 array of nanopillars. The decryptor uses the metasurface to obtain the final transmitted information in two steps.

[0074] Step S5: The specific process of decryption is as follows: 1. The decryptor needs to use different optical keys to extract the high-resolution images encrypted in all channels, which is the basis for accurate information extraction. Considering the case of a higher key level, at a wavelength of λ1=633nm, in order to observe the hidden images in two different channels, it is necessary to insert an optical polarizer and analyzer before and after the metasurface to control the polarization direction of the incident light and the transmitted light respectively, and generate two images under two non-orthogonal polarization light paths (i.e., the first meta-image: θ1= 30° and θ2= 75°, the second meta-image: θ1= -15° and θ2= 30°), as shown in Figure 1. Fig.12 and Fig.13 Considering the case of a lower key level, the encrypted third meta-image can be observed under the wavelength λ2=750nm and any polarization state of light incident, as shown in Fig.14 As shown, by incident light of arbitrary polarization, the third meta-image can be directly obtained from the outgoing light intensity distribution.

[0075] 2. If Fig.15 As shown, the algorithm is used to extract and restore information by combining full-channel optical images. The decryptor first obtains the information extraction and recovery parameter 0.4214 by scanning the first super-structured image, which is crucial to the final accurate acquisition of secret information.

[0076] The specific process of secret information extraction and recovery is as follows: The decryptor needs to perform binarization and run-length encoding on the second and third super-structured images, respectively, to obtain the run-length sequence L of the two images. # 1 and L # 2. Then, the parity of the run length values ​​corresponding to the same even position in the two run sequences is compared at the same time. When the parity is the same, the information binary bit extracted from the position is 0, otherwise 1. When the extracted position exceeds the sequence L # 1, the information will only be in the sequence L # 2. When L # When the run length value of the extraction position in 2 is an even number, the information bit extracted from the position is 0, otherwise it is 1.

[0077] After all the information is extracted, the hidden scrambled secret information is reconstructed and subjected to an XOR logic operation with the iterative sequence generated by the parameter string 0.4214 to recover the hidden secret information.

[0078] It is worth mentioning that the three meta-images encrypted in the metasurface play an equally important role in the final extraction and recovery of secret information. Although the acquisition of secret information only requires two steps, if any of the images is not correctly acquired during the optical decryption of the metasurface, or if the information encryption and decryption process is unclear, the secret information will ultimately not be accurately extracted.

[0079] Most previous optical encryption works based on metasurfaces have used the different responses of metasurfaces to different optical lighting conditions (optical keys) to directly encrypt secret information by imaging, ignoring the metasurface's ultra-high-resolution image display and its advantages in multi-channel joint control.

[0080] Based on the ultra-high resolution image display advantage of the metasurface, the present invention introduces steganography with images as carriers into the field of optical encryption, uses multiple images to disperse and carry secret information, and then encodes multiple images carrying secret information into optical images in the multi-channel metasurface for encrypted transmission. The designed multi-channel metasurface with wavelength and polarization multiplexing also gives different levels of optical keys to the carrier image embedded with secret information, further increasing the security of secret information. In addition, when extracting secret information, it is necessary to use optical keys to obtain the encrypted image information in all channels, and then extract and decode the secret information in conjunction with the encrypted optical images in all channels, giving full play to the advantages of the metasurface in multi-channel joint regulation.

[0081] Embodiment 2 The purpose of this embodiment is to provide an optical encryption steganography system based on a multi-channel metasurface, comprising: The channel construction module is configured to: construct a dual-structure non-spatial multiplexed three-channel metasurface according to the material properties of the dual-wavelength metasurface; The hyperstructured image acquisition module is configured to: acquire secret information, perform scrambling preprocessing, obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first hyperstructured image; Based on the run-length coding steganographic algorithm, two carrier images are selected. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images, and the images are reconstructed to obtain the second and third super-images embedded with the secret information. The optical encryption module is configured to respectively encode the first meta-image, the second meta-image and the third meta-image into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

[0082] Embodiment 3 The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0083] Embodiment 4 The purpose of this embodiment is to provide a computer-readable storage medium.

[0084] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0085] The steps involved in the apparatus of the above embodiment correspond to the method embodiment 1, and the specific implementation method can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0086] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0087] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. An optical encryption steganography method based on a multi-channel metasurface, characterized in that: include: According to the material properties of the dual-wavelength metasurface, a dual-structure non-spatial multiplexing three-channel metasurface is constructed; Acquire secret information, perform scrambling preprocessing to obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first hyperstructured image; Based on the run-length coding steganographic algorithm, two carrier images are selected. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images, and the images are reconstructed to obtain the second and third super-images embedded with the secret information. The first meta-image, the second meta-image and the third meta-image are respectively encoded into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

2. The optical encryption steganography method based on a multi-channel metasurface as claimed in claim 1, characterized in that: According to the material properties of the dual-wavelength metasurface, a dual-structure non-spatial multiplexing three-channel metasurface is constructed, and the specific steps are as follows: A dual-wavelength metasurface is constructed by two different-sized hydrogenated amorphous silicon nanorods on a glass substrate; Based on the material properties of the dual-wavelength metasurface, a working wavelength λ1 and a working wavelength λ2 are selected; At the working wavelength λ1, the two nanorods of different sizes are used as nanopolarizers, a polarizer and an analyzer are placed in front and behind them respectively, and two non-orthogonal polarization light paths are constructed by adjusting the orientation angle of the nanorods and the directions of the polarizer and the analyzer, which are defined as the first channel and the second channel respectively; At the working wavelength λ2, a third channel is constructed according to the different transmission light intensities of the two nanorods of different sizes.

3. The optical encryption steganography method based on a multi-channel metasurface as claimed in claim 1, characterized in that: The specific steps of obtaining the second super-structured image and the third super-structured image embedded with secret information are: selecting two carrier images, defined as a first carrier image and a second carrier image; For the first carrier image, white pixels thereof are represented as 1, black pixels thereof are represented as 0, and the first carrier image is scanned column by column to convert its dimension into a continuous sequence of 01; Performing run-length coding on the obtained continuous 01 sequence, replacing continuous black and white pixels with the number of times they appear; all run-length values ​​after coding constitute a run-length sequence and are named L1; The run-length sequence formed by run-length encoding the second carrier image is named L2; Performing scrambling preprocessing on the embedded secret information to obtain scrambled secret information; Scanning the scrambled secret information column by column to obtain a 01 sequence to be embedded; The information in the 01 sequence to be embedded is embedded into the running sequence L1 and L2 in a dispersed manner according to the bit, so as to obtain the running sequence after the information is embedded; The game sequence after the embedded information is represented as L # 1 and L # 2.

4. The optical encryption steganography method based on a multi-channel metasurface as claimed in claim 3, characterized in that: The image reconstruction is specifically to reconstruct the game sequence L after the embedded information # 1 and L # 2 respectively perform the inverse process of run-length encoding, and recover the continuous black and white pixels by decoding the run-length values ​​in the run sequence, and then reconstruct the second super-image and the third super-image after embedding the secret information.

5. The optical encryption steganography method based on a multi-channel metasurface as claimed in claim 1, characterized in that: The scrambling preprocessing is specifically to use logistic mapping to generate an iterative sequence with non-periodic and non-convergent properties to perform scrambling preprocessing on the secret information.

6. The optical encryption steganography method based on a multi-channel metasurface as claimed in claim 3, characterized in that: The information in the 01 sequence to be embedded is embedded bit by bit in the play sequence L1 and L2 to obtain the play sequence after the information is embedded, which is specifically: When embedding, first detect the run length values ​​corresponding to the same even positions in L1 and L2. When the embedded information bit is 0, modify the larger value of the two to make them have the same parity; when the information bit is 1, also modify the larger value of the two to make them have different parities; when the position embedded in the run sequence exceeds the length of L1, the remaining information will only be embedded in L2. At this time, when the information bit is 0, the run length value of the corresponding position in L2 is modified to an even number; otherwise, it is modified to an odd number; when the parity and the value to be embedded meet the rules, no modification is made.

7. The optical encryption steganography method based on a multi-channel metasurface as claimed in claim 1, characterized in that: Decrypting the encrypted first meta-image, second meta-image, and third meta-image, including: obtaining the working wavelength used in encryption, obtaining the first meta-image and the second meta-image by adjusting the directions of the polarizer and the analyzer at the working wavelength λ1, and directly obtaining the third meta-image from the output light intensity distribution by incident arbitrary polarized light at the working wavelength λ2; Scanning the first hyperstructure image to obtain parameters for extracting and recovering the secret information; The acquired second super-frame image and the third super-frame image are binarized and run-length encoded respectively to obtain the run-length sequence L of the second super-frame image and the third super-frame image. # 1 and L # 2; Compare the program sequence L # 1 and L # 2, the parity of each run length value corresponding to the same even position, and information extraction; After all the information is extracted, the hidden scrambled secret information is reconstructed and subjected to an XOR logic operation with the iterative sequence generated by the parameter string to recover the steganographic secret information.

8. An optical encryption steganography system based on a multi-channel metasurface, characterized in that: include: The channel construction module is configured to: construct a dual-structure non-spatial multiplexed three-channel metasurface according to the material properties of the dual-wavelength metasurface; The hyperstructured image acquisition module is configured to: acquire secret information, perform scrambling preprocessing, obtain scrambled secret information, generate a QR code using parameters extracted and recovered from the secret information, and obtain a first hyperstructured image; Based on the run-length coding steganographic algorithm, two carrier images are selected. According to the parity of the pixels of the two carrier images, the scrambled secret information is scattered and embedded into the run-length sequence of the two carrier images, and the images are reconstructed to obtain the second and third super-images embedded with the secret information. The optical encryption module is configured to respectively encode the first meta-image, the second meta-image and the third meta-image into the dual-structure non-spatial multiplexed three-channel metasurface to realize optical encryption.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of the method described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 7 are performed.

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