Optical steganography method based on structural color, product and preparation method thereof

Abstract

The application discloses an optical steganography method based on structural color, a product and a preparation method thereof, and relates to the technical field of information steganography. The optical steganography method based on structural color comprises the following steps: based on the thin film interference principle, in the visible light range, with the change of the layer thickness of the layered nanostructure, the structural color presented by the layered nanostructure will present periodic cyclic change; when the plaintext and the background respectively present the same or similar structural color by the nanostructure with different layer thickness, the steganography of the plaintext information is realized. Through the accurate regulation of the thickness of the layered nanostructure, the color matching of the structural color in the plaintext and the background area is realized, the difficulty of plaintext encryption is effectively reduced, the method can be used for sensitive information transmission, and can also be applied to daily commodity anti-counterfeiting. Meanwhile, the method is difficult to be characterized even in the nanometer scale, and is not easy to attract the attention of an attacker.

Description

Technical Field

[0001] This invention relates to the field of information steganography technology, and more specifically, to an optical steganography method, product, and preparation method based on structural colors. Background Technology

[0002] In this era of advanced information technology, sensitive information such as copyright identification or user identification is usually encrypted before being sent. Conventional encryption methods require complex algorithms. Currently, mainstream information steganography techniques mainly target the processing of digital images or pictures. Each existing technical solution has its own advantages and disadvantages: Metadata modification: In addition to storing pixel information, image files also need to store some additional descriptive information. Therefore, the file format specifies certain characters to mark specific metadata starting points. This method does not lose image quality, but for information protection reasons, it removes some specific characters from the file format, making this steganography method vulnerable to attack; Bit manipulation: Utilizing the rich information inherent in the image itself, minor modifications can be made without affecting the overall image quality. Visual effects: Steganography methods based on rich information content are not easily attacked, but they will modify the visual quality of the image to some extent. Furthermore, for images with insufficient content, such as large areas of solid color backgrounds, this method is easily cracked. Frequency domain watermarking: This method uses pixel Fourier transform to add watermarks to frequency domain data for information steganography. This method has little impact on the visual effects of the image and has good restoration effects against various image rewriting attacks. However, it cannot directly superimpose watermarks on specific areas of the frequency domain, which would cause significant damage to the original image. Instead, the watermark image needs to be encoded so that it is evenly distributed across frequencies, increasing the difficulty of steganography. It is evident that existing steganography methods all introduce some feature; the difference lies in the salience of this feature. This requires making the plaintext before and after encryption as indistinguishable as possible, thereby achieving information hiding and transmission. Summary of the Invention

[0003] The problem addressed by this invention is how to improve the application limitations caused by the low adsorption capacity, poor release stability, and unsatisfactory release effect of most solid carriers in existing steganography techniques.

[0004] To address the aforementioned problems, this invention provides an optical steganography method based on structural color, comprising: based on the principle of thin-film interference, in the visible light range, the structural color of the layered nanostructure will exhibit periodic cyclic changes as the interlayer thickness changes; when the plaintext and background exhibit the same or similar structural color with nanostructures of different interlayer thicknesses, the plaintext information is steganographically embodied.

[0005] Furthermore, within the visible light range, the center wavelength of the structural color reflection peak of the layered nanostructure satisfies the constructive interference formula: , in, Indicates the effective refractive index of the dielectric layer. Indicates the thickness of the dielectric layer in a layered nanostructure. Indicates the resonance order ( , 2, 3…), Indicates the resonant wavelength.

[0006] Furthermore, the nanostructures with different interlayer thicknesses exhibit the same or similar structural colors in different color cycles, and the color difference of the same or similar structural colors is less than 8.

[0007] Furthermore, it also includes decryption, wherein after the plaintext information is steganographically written, the structural parameters are adjusted so that the spectral reflectance peaks of the background and the plaintext are shifted, and the color difference value increases after the spectral shift within the same color gamut in different color cycles, thereby realizing the decryption of the plaintext.

[0008] Furthermore, the structural parameters include the interlayer refractive index of the layered nanostructure.

[0009] The structural color-based optical steganography method described in this invention has the advantage over existing technologies in that the structural color presented by the layered nanostructure changes periodically with the thickness of the interlayers. When the plaintext and background present the same or similar structural color with nanostructures of different interlayer thicknesses, the plaintext information is steganographically etched. Since existing structural color preparation processes are mature, combined with the precise control of the layered nanostructure thickness in this invention, color matching between the plaintext and background areas is achieved. This effectively reduces the difficulty of plaintext encryption while ensuring steganography effectiveness, making it applicable not only to sensitive information transmission but also to everyday product anti-counterfeiting. Furthermore, this method only introduces the interlayer thickness of different layered nanostructures as a feature difference during plaintext encryption, which is difficult to characterize even at the nanoscale, making it less likely to attract the attention of attackers.

[0010] An optical steganography product based on structural colors, based on the optical steganography method based on structural colors as described above, includes a metal A layer, a dielectric layer and a metal B layer connected in sequence. Incident light is reflected at the junction of the metal A layer and the dielectric layer, and at the junction of the dielectric layer and the metal B layer. Interference occurs between the reflected light, and an emission peak appears.

[0011] Furthermore, metal A is high-purity aluminum foil, the dielectric layer is a porous alumina film, and metal B is silver.

[0012] The optical steganography product based on structural color described in this invention utilizes the interference of reflected light at the interface of different materials to produce emission peaks and form structural colors. Since different reflection peak positions can correspond to the same or similar structural colors, the structure is simple and easy to prepare while achieving optical steganography effect.

[0013] A method for fabricating a structure-color-based optical steganography product, based on the structure-color-based optical steganography product described above, includes the following steps: Step 1: Electrochemically oxidize the high-purity aluminum foil to grow a porous alumina film of a certain thickness on the surface of the high-purity aluminum foil. Step 2: Attach a photomask to the surface of the porous alumina film, and use a laser to engrave a pattern corresponding to the plaintext on the photomask, so that the porous alumina film under the pattern is exposed; Step 3: The porous alumina film from Step 2 is subjected to electrochemical oxidation again, so that the exposed portion of the porous alumina film continues to grow to the preset thickness. All residual masks are removed, and a silver layer is deposited on the surface of the porous alumina film using thermal evaporation technology to complete the preparation of the optical steganography product.

[0014] Furthermore, it also includes changing the refractive index of the porous alumina film by adjusting its structural parameters to achieve the decryption of the plaintext.

[0015] Furthermore, the structural parameters of the porous alumina film include the pore size, internal refractive index, and pore spacing of the porous alumina film.

[0016] The advantage of the structural color-based optical steganography product fabrication method described in this invention compared to existing technologies lies in the fact that the structural color presented by the change in the thickness of the porous alumina film will exhibit a periodic cyclical change. When the plaintext and background present the same or similar structural color with porous alumina films of different thicknesses, the plaintext information is steganographically written. Since existing structural color fabrication processes are mature, combined with the precise control of the porous alumina film thickness in this invention, color matching of the structural color in the plaintext and background areas can be achieved. This effectively reduces the difficulty of plaintext encryption while ensuring steganography effectiveness, making it applicable not only to sensitive information transmission but also to everyday product anti-counterfeiting. Furthermore, this method only introduces the interlayer thickness of different porous alumina films as a feature difference during plaintext encryption, which is difficult to characterize even at the nanoscale, making it less likely to attract the attention of attackers. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the thin-film interference principle of the optical stegography product based on structural color in an embodiment of the present invention; Figure 2This is a schematic diagram of the structure of an optical steganography product based on structural color in an embodiment of the present invention; Figure 3 This is a top view of an optical steganography product based on structural colors in an embodiment of the present invention; 1-Plaintext area; 2-Background area; 3-Incident light; 4-Reflected light; 5-Interface 1; 6-Interface 2. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The present invention will be further described in detail below: These embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods are given, but the scope of protection of the present invention is not limited to the following embodiments.

[0019] Specifically, in combination Figure 1 This invention provides an optical steganography method based on structural color, comprising: based on the principle of thin film interference, in the visible light range, the structural color of the layered nanostructure will change periodically with the change of the interlayer thickness. When the plaintext and the background present the same or similar structural color with nanostructures of different interlayer thicknesses, the plaintext information is steganographically written.

[0020] The structural color-based optical steganography method described in this invention utilizes the periodic cyclical change in structural color resulting from variations in the interlayer thickness of layered nanostructures. When the plaintext and background exhibit the same or similar structural colors with nanostructures of different interlayer thicknesses, the plaintext information is steganographically encoded. Since existing structural color fabrication processes are mature, and combined with the precise control of the layered nanostructure thickness in this invention, color matching between the plaintext and background regions is achieved. This effectively reduces the difficulty of plaintext encryption while maintaining steganographic effectiveness, making it applicable not only to sensitive information transmission but also to everyday product anti-counterfeiting. Furthermore, this method introduces only the interlayer thickness of different layered nanostructures as a feature difference during plaintext encryption, making it difficult to characterize even at the nanoscale and less likely to attract the attention of attackers.

[0021] Specifically, when visible light shines on a layered nanostructure, reflection occurs on the upper and lower surfaces, and the reflected light interferes, forming a structural color. As the thickness between the layers of the nanostructure changes, the interference pattern of the reflected light changes, causing the structural color to exhibit a periodic, cyclical variation. When the same or similar structural colors are required, nanostructures with different interlayer thicknesses can be used to achieve steganography of plaintext information in optical vision. It should be noted that the color observed by the human eye depends on the combined effect of all reflection peaks within the visible light spectrum. Therefore, a structural color exhibited by multiple reflection peaks is very likely to be similar to a color exhibited by a single reflection peak. Thus, similar structural colors can correspond to different reflection peak positions.

[0022] It should also be noted that structural colors are produced when light undergoes refraction, diffuse reflection, diffraction, or interference at subwavelength structures, resulting in the enhancement or suppression of specific wavelengths and thus producing various colors. For example, the metallic luster and shimmer of a beetle's body wall are typical examples of structural colors. Due to their advantages such as colorfastness, environmental friendliness, and iridescent effects, structural colors have broad application prospects in display, decoration, and anti-counterfeiting fields. Researching the formation mechanism and applications of structural colors in nature can promote the development of biomimetic structural color processing and micro / nano optical technologies.

[0023] In one specific embodiment, within the visible light range, the center wavelength of the structural color reflection peak of the layered nanostructure satisfies the constructive interference formula: , in, Indicates the effective refractive index of the dielectric layer. Indicates the thickness of the dielectric layer in a layered nanostructure. Indicates the resonance order ( , 2, 3…), Indicates the resonant wavelength.

[0024] Specifically, the effective refractive index of the dielectric layer Under the premise of not changing, the thickness of the dielectric layer of the layered nanostructure Changes affect the resonant wavelength This allows for changes in structural colors, with clear correspondences and easily controllable variables.

[0025] In one specific embodiment, the nanostructures with different interlayer thicknesses exhibit the same or similar structural colors in different color cycles, and the color difference of the same or similar structural colors is less than 8. Thus, by controlling the numerical range of the color difference, the concealment of optical steganography is improved through quantitative control.

[0026] It should be noted that color difference usually refers to the difference in color, which is a quantitative concept in color science. Color difference can be simply calculated using Euclidean distance within a color space, or it can be calculated using the more complex and uniform human perception formula from the International Commission on Illumination (ICILI). In short, it is a numerical value that can measure the difference in color between different colors.

[0027] In one specific embodiment, the method further includes decryption, wherein after the plaintext information is steganographically written, the structural parameters are adjusted so that the spectral reflectance peaks of the background and the plaintext are shifted, and the color difference value increases after the spectral shift within the same color gamut in different color cycles, thereby achieving the decryption of the plaintext.

[0028] Specifically, in this embodiment, the structural parameters affect the emission and interference of the incident light 3, ultimately influencing the emission peak and causing a change in the structural color, thus increasing the color difference value to a level that facilitates discrimination. The structural parameters here are selected based on the specific structure; any parameter that effectively affects the emission peak can be included.

[0029] In one specific embodiment, the structural parameters include the interlayer refractive index of the layered nanostructure. This effectively increases color difference, enabling rapid and simple decryption.

[0030] This invention provides an optical steganography product based on structural colors, comprising a metal A layer, a dielectric layer, and a metal B layer connected in sequence. Incident light 3 is reflected at the junction of the metal A layer and the dielectric layer, and at the junction of the dielectric layer and the metal B layer. The reflected light 4 interferes with each other and an emission peak appears.

[0031] The optical steganography product based on structural colors described in this embodiment of the invention utilizes the interference of reflected light 4 at the interface of different materials, such as... Figure 1 As shown, interface 5 is the junction of the metal A layer and the dielectric layer, where incident light is reflected. Interface 6 is the junction of the dielectric layer and the metal B layer, where incident light undergoes secondary reflection. The reflected light from the two interfaces interferes and emission peaks appear, forming structural colors. Since different reflection peak positions can correspond to the same or similar structural colors, the structure is simple and easy to fabricate while achieving optical steganography.

[0032] In one specific embodiment, metal A is high-purity aluminum foil, the dielectric layer is a porous alumina film, and metal B is silver. Therefore, the materials are readily available, and the steganography effect is significant.

[0033] Specifically, starting with violet, corresponding to the short-wavelength visible light band, the thickness of the porous alumina film is increased from 230 nm to 530 nm in increments of 10 nm. The structural colors of the optical steganography product exhibit a periodic cyclical characteristic and can cover all specific color chromaticities within the color band. Each color group transitioning from the blue to the red zone can be called a color cycle, providing the color basis for optical steganography.

[0034] This invention also provides a method for preparing an optical stegographic product based on structural colors, comprising the following steps: Step 1: Electrochemically oxidize the high-purity aluminum foil to grow a porous alumina film of a certain thickness on the surface of the high-purity aluminum foil. Step 2: Attach a photomask to the surface of the porous alumina film, and use a laser to engrave a pattern corresponding to the plaintext on the photomask, so that the porous alumina film under the pattern is exposed; Step 3: The porous alumina film from Step 2 is subjected to electrochemical oxidation again, so that the exposed portion of the porous alumina film continues to grow to the preset thickness. All residual masks are removed, and a silver layer is deposited on the surface of the porous alumina film using thermal evaporation technology to complete the preparation of the optical steganography product.

[0035] Combination Figure 2 and Figure 3 The method for preparing optical steganography products based on structural colors described in this invention achieves steganography by varying the thickness of a porous alumina film, resulting in a periodic and cyclical change in structural color. When the plaintext and background exhibit the same or similar structural colors using porous alumina films of different thicknesses, the plaintext information is steganographically written. Since existing structural color preparation processes are mature, and combined with the precise control of the porous alumina film thickness in this invention, color matching between the plaintext and background areas is achieved. This effectively reduces the difficulty of plaintext encryption while ensuring steganography effectiveness, making it applicable not only to sensitive information transmission but also to everyday product anti-counterfeiting. Furthermore, this method only introduces the interlayer thickness of different porous alumina films as a feature difference during plaintext encryption, which is difficult to characterize even at the nanoscale, thus minimizing the risk of attracting attackers' attention.

[0036] Specifically, high-purity aluminum foil is placed in a suitable electrolyte as the anode and electrochemically oxidized under specific conditions and an applied current. The electrolyte can be sulfuric acid, chromic acid, or oxalic acid, causing a porous alumina film of a certain thickness to grow on the surface of the high-purity aluminum foil. The thickness of this porous alumina film corresponds to the desired background structural color. A mask is then attached to the surface of the porous alumina film, and a pattern corresponding to the plaintext is engraved on the mask using a laser, exposing the porous alumina film beneath the pattern. Electrochemical oxidation is then performed again, allowing the exposed portion of the porous alumina film to continue growing to a predetermined thickness, which also corresponds to the desired structural color of the plaintext. All remaining mask material is then removed, and a silver layer is deposited on the surface of the porous alumina film using thermal evaporation technology, completing the optical steganography product and achieving optical steganography of the plaintext. In summary, using existing mature technologies such as electrochemical oxidation and laser engraving, optical steganography products can be rapidly prepared with high precision and a simple preparation method.

[0037] In one specific embodiment, the method further includes adjusting the structural parameters of the porous alumina film to change its refractive index, thereby enabling the decryption of the plaintext. This is achieved by influencing the interference of visible light through refractive index, causing a shift in the spectral reflection peak, and thus increasing the color difference between the plaintext structural color and the background structural color, enabling rapid decryption.

[0038] In one specific embodiment, the structural parameters of the porous alumina film include the pore size, internal refractive index, and pore spacing of the porous alumina film.

[0039] Specifically, the encrypted product can be further modified by immersing it in a phosphoric acid solution to increase the pore size of the porous alumina film, or the encrypted product can be immersed in a refractive index solution to change the refractive index within the pores of the porous alumina film. By altering the refractive index and pore size of the porous alumina film, the color correspondence between the background structure and the pattern structure can be broken, thus decrypting the encrypted product. The decryption process is simple and has few interfering factors.

[0040] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An optical steganography method based on structural colors, characterized in that, The optical steganography method uses an optical steganography product, which includes a metal A layer, a dielectric layer, and a metal B layer connected in sequence. Incident light is reflected at the junction of the metal A layer and the dielectric layer, and at the junction of the dielectric layer and the metal B layer. Interference occurs between the reflected light, and a reflection peak appears. The metal A layer is a high-purity aluminum foil, the dielectric layer is a porous alumina film, and the metal B layer is silver. Based on the principle of thin-film interference, within the visible light range, the structural color of layered nanostructures will exhibit periodic cyclic changes as the thickness of the dielectric layer varies. When the plaintext and background exhibit the same or similar structural colors with nanostructures of different dielectric layer thicknesses, the plaintext information is steganographically written. The same or similar structural colors with nanostructures of different dielectric layer thicknesses refer to the same or similar structural colors within different color cycles. Decryption involves adjusting the structural parameters of the dielectric layer after steganography. This adjustment includes adjusting the effective refractive index of the dielectric layer, causing a shift in the spectral reflection peaks of both the background and the plaintext. The color difference value increases after the spectral shift within the same color gamut in different color cycles, thus enabling the decryption of the plaintext.

2. The optical steganography method according to claim 1, characterized in that, In the visible light range, the center wavelength of the structural color reflection peak of the layered nanostructure satisfies the constructive interference formula: in, Indicates the effective refractive index of the dielectric layer. Indicates the thickness of the dielectric layer in a layered nanostructure. Indicates the resonance order ( , 2, 3…), Indicates the resonant wavelength.

3. The optical steganography method according to claim 1, characterized in that, The preparation of the optical stegographic product according to claim 1 includes the following steps: Step 1: Electrochemically oxidize the high-purity aluminum foil by placing it in an electrolyte as the anode. The electrolyte is sulfuric acid, chromic acid, or oxalic acid, causing a porous alumina film of a certain thickness to grow on the surface of the high-purity aluminum foil. Step 2: Attach a mask to the surface of the porous alumina film, and use a laser to engrave a pattern corresponding to the plaintext on the mask, so that the porous alumina film under the pattern is exposed; Step 3: The porous alumina film from Step 2 is subjected to electrochemical oxidation again, so that the exposed portion of the porous alumina film continues to grow to the preset thickness. All residual mask plates are removed, and a silver layer is deposited on the surface of the porous alumina film using thermal evaporation technology to complete the preparation of the optical steganography product.

4. The optical steganography method according to claim 3, characterized in that, It also includes changing the effective refractive index of the porous alumina film by adjusting the structural parameters of the porous alumina film, thereby achieving the decryption of the plaintext.

5. The optical steganography method according to claim 4, characterized in that, The structural parameters of the porous alumina film include the pore size and pore spacing.

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