Anti-counterfeiting label based on reconfigurable laser scattering optical PUF and its authentication method

Abstract

The present invention provides an anti-counterfeiting label based on a reconfigurable laser scattering optical PUF and an authentication method therefor. The anti-counterfeiting label includes a reversible phase change layer and a disordered scattering medium layer. The thickness of the reversible phase change layer is 50 nm to 1000 nm, and the average particle size is 20 nm to 500 nm. The authentication method includes: inducing a reversible phase change in the anti-counterfeiting label of the reconfigurable laser scattering optical PUF to complete the speckle reconstruction of the anti-counterfeiting label, and digitally processing the speckle pattern before and after the reconstruction of the anti-counterfeiting label to extract a key, obtaining a registration key K i and storing it in a database; obtaining an authentication key K formed after the speckle reconstruction of the anti-counterfeiting label to be authenticated x . When the Hamming distance between (K x , K i ) is less than a preset threshold T, the user identity authentication is successful. The anti-counterfeiting authentication label formed by the present invention has the characteristics of good repeatability, high coding capacity, large challenge-response regulation freedom, and high security.

Description

Technical Field

[0001] The present invention relates to the field of anti-counterfeiting security. Specifically, it relates to an anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF, and an authentication method for an anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF. Background Art

[0002] Currently, the main anti-counterfeiting technologies adopted at home and abroad include oil ink printing, engraving printing, laser holography, etc. Oil ink printing anti-counterfeiting is an optical anti-counterfeiting method that uses various fluorescent substances and the basic principles of light reflection, refraction, transmission, interference, etc. By making a unique anti-counterfeiting label for repeated authentication and irradiating it at a specific wavelength to display the encoded information. However, the preparation of such anti-counterfeiting labels all depends on a definite production process. Although these labels have low costs, their simple and repeatable preparation processes and regular decoding mechanisms often give many counterfeiters opportunities. Counterfeiters can still copy and forge these labels, thus rendering the anti-counterfeiting effect ineffective.

[0003] A physical unclonable function (PUF) refers to a technology that uniquely identifies using the internal physical structure of a substance. Each input challenge will obtain a unique and unpredictable response. In recent years, PUF has developed into a reliable authentication and anti-counterfeiting system. The extremely complex self-structure of PUF makes it impossible for counterfeiters to reproduce another exactly identical PUF even using the same process, having excellent uniqueness. Among many types of PUFs, optical PUFs have low preparation costs, simple and rapid response reading, and have received extensive attention and research. Especially for three-dimensional disordered particle PUFs based on laser scattering, due to the extreme sensitivity of the laser to the internal structure of the scatterer, a slight change in the internal structure of the scatterer will result in completely different laser speckles, making it more difficult for counterfeiters to forge. However, once the laser-scattering type PUF is manufactured, its disordered structure is determined, so it exhibits fixed challenge-response behavior, resulting in relatively limited coding capacity and the risk of being attacked by modeling. For example, there are problems of unchangeable information and low coding ability in the laser speckle pattern of transparent materials and the laser signal on the paper surface.

[0004] Therefore, it is of great significance to research and develop laser-scattering type PUFs with greater challenge-response regulation freedom and higher security. Summary of the Invention

[0005] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies existing in the prior art. For example, one of the purposes of the present invention is to provide a reversible R-PUF anti-counterfeiting authentication label with good repeatability, high coding capacity, and large challenge-response regulation freedom.

[0006] To achieve the above object, on the one hand, the present invention provides an anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF. The anti-counterfeiting label may include a reversible phase change layer and a disordered scattering medium layer. The reversible phase change layer is attached to the upper surface of the disordered scattering medium layer, and the thickness of the reversible phase change layer is 50 nm to 1000 nm, and the average particle size is 20 nm to 500 nm.

[0007] In an exemplary embodiment of the anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF of the present invention, the reversible phase change layer may include VO 2 and GST.

[0008] In an exemplary embodiment of the anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF of the present invention, the way for the reversible phase change layer to undergo a phase change may be thermal stimulation, electrical stimulation, optical stimulation or strain stimulation.

[0009] In an exemplary embodiment of the anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF of the present invention, the disordered scattering medium layer may be TiO 2 , ZrO 2 or ZnO.

[0010] In an exemplary embodiment of the anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF of the present invention, the thickness of the reversible phase change layer may be 150 nm to 450 nm, and the average particle size may be 200 nm to 500 nm.

[0011] In an exemplary embodiment of the anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF of the present invention, the Hamming distance of the reversible phase change layer before and after reconstruction can be between 0.4 and 0.6.

[0012] On the other hand, the present invention provides an authentication method for an anti-counterfeiting label based on a reconfigurable laser-scattering optical PUF. The authentication method may include: inducing a reversible phase change in the reversible phase change layer on the anti-counterfeiting label as described above to complete the speckle reconstruction of the anti-counterfeiting label, and obtaining the speckle pattern before reconstruction and the speckle pattern after reconstruction; respectively performing digital processing on the speckle pattern before reconstruction and the speckle pattern after reconstruction of the anti-counterfeiting label to extract keys, obtaining the key K i (L) before reconstruction and the key K i (H) after reconstruction, performing a Boolean operation on the key before reconstruction and the key after reconstruction to form a registration key K i , and storing it in the database of the laser speckle reading device; using the laser speckle reading device to obtain the key K x (L) before reconstruction and the key K x (H) after reconstruction of the anti-counterfeiting label to be authenticated, and performing a Boolean operation to form a key K x, calculate the key K to be authenticated x with the registered key K i to calculate the Hamming distance. When the Hamming distance between (K x , K i ) is less than the preset threshold T, the user identity authentication is successful; otherwise, the user identity authentication fails.

[0013] In an exemplary embodiment of the authentication method of the anti-counterfeiting label based on the reconfigurable laser-scattering optical PUF of the present invention, the preset threshold T can be 0.1 to 0.3.

[0014] In an exemplary embodiment of the authentication method of the anti-counterfeiting label based on the reconfigurable laser-scattering optical PUF of the present invention, the authentication method may further include: determining whether the key similarity change curve feature of the anti-counterfeiting label to be authenticated under the stimulation condition matches the key similarity change curve feature of the registered anti-counterfeiting label in the database under the stimulation condition. If so, the user identity authentication is successful; otherwise, the user identity authentication fails.

[0015] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0016] (1) The present invention proposes a reconfigurable laser-scattering optical PUF, which utilizes the reversible phase change characteristic of VO 2 to realize the reconstruction of the laser-scattering PUF, effectively solving the problems of fixed challenge-response characteristics and limited coding capacity of traditional laser-scattering PUFs;

[0017] (2) The anti-counterfeiting authentication label based on the reconfigurable laser-scattering optical PUF formed by the present invention has the characteristics of good repeatability, high coding capacity, large challenge-response regulation freedom, and high security;

[0018] (3) The anti-counterfeiting authentication method based on the reconfigurable laser-scattering optical PUF formed by the present invention completes user identity authentication from two encryption dimensions of "laser-speckle" reconstruction and similarity hysteresis curve features, effectively preventing attacks by forging speckles and increasing the difficulty for counterfeiters to crack password information. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Through the following description with reference to the drawings, the above and other objects and / or features of the present invention will become clearer, where:

[0020] Figure 1 shows a schematic flowchart of the anti-counterfeiting authentication method according to an exemplary embodiment of the present invention.

[0021] Figure 2 shows a 396 nm thick VO according to an exemplary embodiment of the present invention 2XRD pattern of the thin film.

[0022] Figure 3A Shows VO of an exemplary embodiment of the present invention 2 Temperature-dependent Raman spectra of the thin film; Figure 3B Shows VO of an exemplary embodiment of the present invention 2 Temperature-dependent Fourier transform infrared spectra of the thin film.

[0023] Figure 4 Shows 396 nm thick VO of an exemplary embodiment of the present invention 2 Surface topography and cross-sectional SEM images of the thin film.

[0024] Figure 5 Shows 396 nm thick VO of an exemplary embodiment of the present invention 2 Statistical chart of the size distribution of surface particles in the SEM image of the thin film.

[0025] Figure 6A Shows the speckle pattern of the laser scattering type PUF of an exemplary embodiment of the present invention at 25 °C; Figure 6B Shows the speckle pattern of the laser scattering type PUF of an exemplary embodiment of the present invention at 75 °C; Figure 6C Shows the speckle pattern of 396 nm VO 2 / R-PUF at 25 °C; Figure 6D Shows 396 nm VO 2 / R-PUF at 75 °C.

[0026] Figure 7A Shows the schematic diagram of the Hamming distance between the speckle at 25 °C and the speckles at other temperatures of an exemplary embodiment of the present invention; Figure 7B Shows the schematic diagram of the similarity between the speckle at 25 °C and the speckles at other temperatures of an exemplary embodiment of the present invention; Figure 7C Shows the similarity heat map between different temperatures of an exemplary embodiment of the present invention.

[0027] Figure 8 Shows VO of an exemplary embodiment of the present invention 2 / R-PUF accuracy curve schematic diagram after multiple authentications.

[0028] Figure 9 Shows VO of an exemplary embodiment of the present invention 2 / R-PUF cyclic stability curve schematic diagram.

[0029] Figure 10A Shows VO of an exemplary embodiment of the present invention2 Similarity hysteresis curve during the heating and cooling processes of the / R-PUF; Figure 10B Shows the VO of an exemplary embodiment of the present invention 2 Infrared light transmittance hysteresis curve of the thin film; Figure 10C Shows the VO of an exemplary embodiment of the present invention 2 Hot spot map of the similarity between speckles at various temperatures during the cooling process of the / R-PUF.

[0030] Figure 11A Shows the 194nm VO of another exemplary embodiment of the present invention 2 Cross-sectional SEM image of the thin film; Figure 11B Shows the 194nm VO of another exemplary embodiment of the present invention 2 Surface SEM image of the thin film; Figure 11C Shows the 194nm VO of another exemplary embodiment of the present invention 2 Statistical distribution map of the corresponding surface particle sizes of the thin film.

[0031] Figure 12A Shows the different thickness VO of another exemplary embodiment of the present invention 2 Schematic diagram of the Hamming distance curve of the / R-PUF; Figure 12B Shows the different thickness VO of another exemplary embodiment of the present invention 2 Schematic diagram of the similarity curve of the / R-PUF; Figure 12C Shows the 194nm VO of another exemplary embodiment of the present invention 2 Schematic diagram of the similarity hysteresis curve of the / R-PUF.

[0032] Figure 13A Shows the 394nm VO obtained by the two-step preparation method of another exemplary embodiment of the present invention 2 Cross-sectional SEM image of the thin film; Figure 13B Shows the 394nm VO obtained by the two-step preparation method of another exemplary embodiment of the present invention 2 Surface SEM image of the thin film; Figure 13C Shows the 394nm VO obtained by the two-step preparation method of another exemplary embodiment of the present invention 2 Statistical distribution map of the corresponding surface particle sizes of the thin film.

[0033] Figure 14A Shows the different surface morphology VO of another exemplary embodiment of the present invention 2 Schematic diagram of the Hamming distance curve of the / R-PUF; Figure 14B Shows the different surface morphology VO of another exemplary embodiment of the present invention 2Schematic diagram of the similarity curve of VO / R-PUF; Figure 14C Shows the similarity hysteresis curve diagram of 394nm VO / R-PUF obtained by the two-step preparation method of another exemplary embodiment of the present invention. 2 Detailed implementation manners

[0034] Hereinafter, the anti-counterfeiting label based on the reconfigurable laser scattering optical PUF and its authentication method of the present invention will be described in detail in conjunction with exemplary embodiments.

[0035] It should be noted that in this article, a physical unclonable function (PUF) refers to a physical entity that cannot be precisely replicated; a reconfigurable physical unclonable function (R-PUF) refers to that the internal structure of the PUF or the information generated by it can change dynamically; a laser scattering type PUF refers to being composed of a disordered scattering medium and being able to strongly scatter a laser to obtain laser speckles; VO / R-PUF refers to the R-PUF obtained after structuring a VO thin film with a laser speckle PUF. The Hamming Distance is a way to measure the degree of speckle reconstruction, and its value ranges from 0 to 1. The Hamming Distance between ideally completely independent speckles is 0.5. The Inter-Hamming Distance (Inter-HD) refers to the Hamming Distance of speckles between different PUFs and can be used to measure the degree of speckle reconstruction. The Intra-Hamming Distance (Intar-HD) refers to the Hamming Distance of speckles obtained by the same PUF at different times and can be used for the repeatability of the PUF. Similarity refers to the degree of similarity between speckle patterns and can be used to measure the degree of speckle reconstruction. Its value ranges from 0 to 1. The lower the similarity value, the more obvious the speckle reconstruction. 2 2

[0036] The inventors have found through research that: the three-dimensional disordered structure of traditional laser scattering PUFs is fixed, and they can only exhibit fixed challenge-response behaviors, which are not only vulnerable to reverse engineering modeling attacks but also have low coding capabilities. However, the phase change of a reversible phase change layer (for example, a VO thin film) can cause the reconstruction of laser speckles, changing the originally fixed challenge-response behaviors of the laser scattering PUF, thereby increasing the coding capacity of the R-PUF. At the same time, the temperature hysteresis curve of the reversible phase change layer phase change also provides a new idea for enhancing anti-counterfeiting and information security. 2

[0037] To achieve the above object, on the one hand, the present invention provides an anti-counterfeiting label based on a reconfigurable laser scattering optical PUF.

[0038] In an exemplary embodiment of the present invention, the anti-counterfeiting label based on the reconfigurable laser scattering optical PUF includes a reversible phase change layer and a disordered scattering medium layer. The reversible phase change layer is attached to the upper surface of the disordered scattering medium layer, and the thickness of the reversible phase change layer is 50 nm to 1000 nm, and the average particle size is 20 nm to 500 nm. For example, the thickness of the reversible phase change layer can be 80 nm, 150 nm, 250 nm, 450 nm, 750 nm, 850 nm, 1000 nm, etc., and the average particle size is 90 nm, 150 nm, 200 nm, 300 nm, 450 nm, 500 nm, etc.

[0039] Among them, the reversible phase change layer is composed of a material with phase change function, which can be VO 2 or GST.

[0040] The disordered scattering medium layer is composed of a high refractive index material, which can be TiO 2 、ZrO 2 or ZnO.

[0041] Furthermore, the thickness of the reversible phase change layer can be 150 nm to 450 nm. This is because for short-wavelength lasers, the reversible phase change layer of the anti-counterfeiting label does not need to be very thick to achieve a good speckle reconstruction effect, but for long wavelengths, it is required that the reversible phase change layer of the anti-counterfeiting label has a certain thickness.

[0042] Furthermore, the average particle size of the reversible phase change layer can be 200 nm to 500 nm. This is because the average particle size of the reversible phase change layer is one of the factors affecting the laser speckle reconstruction degree of the reconfigurable laser scattering optical PUF. When the phase change material particles on the reversible phase change layer of the anti-counterfeiting label are larger, the scattering effect of itself is better, and the anti-counterfeiting performance of the formed anti-counterfeiting label is stronger.

[0043] Of course, the thickness of the reversible phase change layer of the anti-counterfeiting label will also affect its own scattering effect to a certain extent. Therefore, as long as it is ensured that the thickness of the reversible phase change layer of the anti-counterfeiting label is appropriate and the particle size of the phase change material is also appropriate, so that the Hamming distance between the reversible phase change layer before and after reconstruction can be between 0.4 and 0.6, that is, the Hamming distance between the speckles before and after reconstruction can be close to 0.5, which is beneficial to realizing completely independent reconstructed speckles, thereby enhancing the security of the anti-counterfeiting label.

[0044] It should be noted that the reversible phase change material has a reconfigurable microstructure and optical properties, and is an ideal material for preparing the reconfigurable optical PUF. The reversible phase change layer refers to a thin film layer formed by a reversible phase change material with reversible insulator-metal transition (IMT) characteristics.

[0045] The determination of reversible phase change materials depends on the following points: ① having the ability to transmit laser both before and after phase change; ② at a specific wavelength position, there are significant changes in optical properties (refractive index) before and after phase change; ③ reversible phase change (i.e., having the same / similar optical properties under the same external conditions).

[0046] For example, the reversible phase change layer can be VO 2 thin film. As a reversible phase change material, VO 2 (M) will undergo a reversible transformation from a monoclinic structure with semiconductor properties to a tetragonal rutile structure with metallic properties at around 68 °C. When stimulated by heat, electricity, light, or strain, VO 2 will undergo this IMT transformation. Due to the existence of reversible phase change, the optical properties such as refractive index and transmittance / reflection rate of VO 2 will change significantly, especially in the infrared band, which provides an effective method for reconstructing the challenge - response characteristics of PUFs.

[0047] Currently, common methods for preparing VO 2 thin films include: sol - gel method, chemical vapor deposition method, pulsed laser deposition method, and magnetron sputtering method.

[0048] On the other hand, the present invention provides an authentication method for anti - counterfeiting labels based on reconfigurable laser - scattering optical PUFs.

[0049] In another exemplary embodiment of the present invention, as Figure 1 shown, an authentication method for anti - counterfeiting labels based on reconfigurable laser - scattering optical PUFs includes the following steps:

[0050] Step S1, inducing a reversible phase change in the reversible phase change layer on the anti - counterfeiting label based on reconfigurable laser - scattering optical PUFs (i.e., the anti - counterfeiting label in the above - mentioned embodiment), completing the speckle reconstruction of the anti - counterfeiting label, and obtaining the speckle pattern before reconstruction and the speckle pattern after reconstruction.

[0051] Step S2, digitally processing the speckle pattern before reconstruction and the speckle pattern after reconstruction of the anti - counterfeiting label respectively to extract keys, obtaining the key K i (L) before reconstruction and the key K i (H) after reconstruction, performing a Boolean operation on the key before reconstruction and the key after reconstruction to form a registration key K i , and storing it in the database of the laser speckle reading device.

[0052] Step S3, placing the anti - counterfeiting label to be authenticated in the laser speckle reading device to obtain the key K x (L) before reconstruction and the key K x (H) after reconstruction, and performing a Boolean operation to form a key K x, calculate the key K to be authenticated x and the registered key K i to calculate the Hamming distance. When the Hamming distance between (K x , K i ) (i.e., the inter-group Hamming distance) is less than the preset threshold T, the user identity authentication is successful; otherwise, the user identity authentication fails. For example, the preset threshold T can be 0.1 to 0.3.

[0053] In another exemplary embodiment of the present invention, an authentication method based on a reconfigurable laser scattering optical PUF also includes the following steps:

[0054] Step S1': Induce the reversible phase change layer on the anti-counterfeiting label in the above embodiment to undergo a reversible phase change, complete the speckle reconstruction of the anti-counterfeiting label, and obtain the speckle pattern before reconstruction and the speckle pattern after reconstruction.

[0055] Step S2': Digitally process the speckle patterns before and after the reconstruction of the anti-counterfeiting label respectively to extract keys, and obtain the key K i (L) before reconstruction and the key K i (H) after reconstruction. Perform a Boolean operation on the key before reconstruction and the key after reconstruction to form the registered key K i , and store it in the database of the laser speckle reading device.

[0056] Step S3': Place the anti-counterfeiting label to be authenticated in the laser speckle reading device to obtain the key K x (L) before reconstruction and the key K x (H) after reconstruction, and perform a Boolean operation to form the key K x to be authenticated. Calculate the Hamming distance between the key K x to be authenticated and the registered key K i . When the Hamming distance between (K x , K i ) (i.e., the inter-group Hamming distance) is less than the preset threshold T, and the key similarity change curve features of the anti-counterfeiting label to be authenticated and the anti-counterfeiting label are exactly the same, the user identity authentication is successful; otherwise, when the Hamming distance between (K x , K i ) (i.e., the inter-group Hamming distance) is greater than or equal to the preset threshold T, and / or the key similarity change curve features of the anti-counterfeiting label to be authenticated and the anti-counterfeiting label do not match, the user identity authentication fails.

[0057] The hysteresis curve existing during the phase change process can also be collected, and then images can be collected at some points on the curve for similarity comparison. The authentication method is the same as the authentication method before / after the phase change.

[0058] It should be noted that although inducing the IMT phase transition in the reversible phase change layer can cause the reconstruction of laser speckles, change the original fixed challenge-response behavior of the laser PUF, and thus increase the R-PUF coding capacity. However, due to the differences in the preparation of the reversible phase change layer itself, although the speckles are reconstructed, the degree of reconstruction is relatively low, and the Hamming distance of the perfectly reconstructed speckles should be around 0.5. The surface topography and surface integrity of the reversible phase change layer are also important factors affecting the degree of laser speckle reconstruction of the reconfigurable laser scattering optical PUF. Specifically, the rougher and more uneven the surface of the reversible phase change layer, the more obvious the speckle reconstruction; and within a certain range, the thicker the thickness of the reversible phase change layer, the more obvious the speckle reconstruction. Therefore, in order to increase the degree of speckle reconstruction and ensure that the speckles before and after reconstruction are completely independent as much as possible, the reversible phase change layer can be pretreated by increasing the thickness, particle size, and surface irregularity of the reversible phase change layer.

[0059] VO 2 Influencing factors such as the thickness and surface topography of the thin film directly determine the 2 VO / R-PUF laser speckle reconstruction degree. For example, 2 the thicker the VO thin film, the more obvious the speckle reconstruction, but the film thickness should not be too thick, otherwise the speckle signal will be too weak to collect information. 2 The rougher and more uneven the surface of the VO thin film, and the larger the particles forming the thin film, the more obvious the speckle reconstruction after phase change.

[0060] To better understand the above exemplary embodiments of the present invention, the following further describes them in conjunction with the accompanying drawings and specific examples.

[0061] Example 1

[0062] In this example, an authentication method for an anti-counterfeiting label based on a reconfigurable laser scattering optical PUF is implemented through the following steps.

[0063] Step1. Complete the preparation of the VO 2 thin film and VO 2 / R-PUF.

[0064] (1) Preparation of the VO 2 thin film

[0065] Using pure metal vanadium as the sputtering target, O 2 as the reaction gas, and Ar as the working gas. Ar is ionized into Ar 3+ in the vacuum chamber, and Ar 3+ collides with the vanadium target under the acceleration of the electric field to obtain large vanadium ions, vanadium atoms, and V atomic clusters. V ions, etc. react with O 2A reaction occurs to generate vanadium oxide. The vanadium oxide is deposited on a substrate with a temperature and annealed to obtain a dense VO 2 (M) thin film.

[0066] The specific process parameters for preparing VO 2 thin film by magnetron sputtering are shown in Table 1. The film growth rate of magnetron sputtering is about The thickness of the thin film can be roughly controlled by controlling the coating time. In this example, a VO 2 thin film with a thickness of 396 nm was prepared.

[0067] Table 1 Specific process parameters for preparing VO 2 thin film by magnetron sputtering

[0068]

[0069]

[0070] Figure 2 The XRD pattern of the VO 2 thin film prepared on the SiO 2 substrate by RF magnetron sputtering. It can be seen from the XRD pattern that the diffraction peaks of the prepared thin film match very well with the VO 2 (M) standard PDF card 43-1051; the diffraction peaks at 27.98°, 37.12°, 42.34°, 55.64° and 57.64° correspond to the (011), (200), (210), (220) and (022) crystal planes of the M-phase VO 2 , indicating that the M-phase VO 2 polycrystalline thin film has been prepared in this example. It can also be seen from the XRD pattern that the crystallization performance of the thin film is very good, and there is a very sharp diffraction peak at the (011) crystal plane corresponding to 27.97°, which is the main direction of film growth. It should be noted that the crystallinity of the VO 2 thin film has an important influence on its phase transition and optical properties. The better the crystallization performance, the more obvious its phase transition characteristics.

[0071] Because the premise for the realization of R-PUF is that the VO 2 thin film has good phase transition characteristics, which leads to a huge change in optical properties after phase transition. Therefore, in order to explore the phase transition characteristics of the VO 2 thin film, the variable-temperature Raman and variable-temperature infrared spectral information of this thin film were collected in this example. From Figure 3A it can be seen that at 25 °C, the spectral information in the experiment is the M-phase VO 2 , and the Raman peaks corresponding to 143 cm -1 , 192 cm -1 , 223 cm -1 , 262 cm-1 , 309 cm -1 , 389 cm -1 , 498 cm -1 and 614 cm -1 is consistent with that reported in the literature. As the temperature increases, the Raman peaks of M-phase VO 2 gradually disappear, indicating that M has begun to slowly transform into the R-phase. At 68 °C and 75 °C, no peaks can be seen in the Raman spectrum, indicating that the VO 2 nanocrystalline thin film has completely undergone a phase change, transforming from the M-phase to the R-phase. Fourier transform infrared spectroscopy shows the relationship between the infrared transmittance of the VO 2 thin film and temperature. As shown in Figure 3B , the maximum transmittance of the VO 2 thin film at 25 °C is 65%, and its transmittance gradually decreases as the temperature increases. When the temperature reaches 75 °C, the transmittance drops to the lowest, only about 20%. Both Raman spectroscopy and Fourier transform infrared spectroscopy prove that the VO 2 thin film used in this example has good phase change properties.

[0072] VO 2 The surface morphology and cross-section SEM of the thin film are shown in Figure 4 . As can be seen from Figure 4 , the thickness of the VO 2 thin film prepared in this example is 396 nm. The thin film is composed of countless irregular particles, with an uneven surface and different sizes. This characteristic is very beneficial for resisting the replication behavior of attackers because the fine particles on the surface of the VO 2 thin film itself will also have a certain scattering effect on the laser. Coupled with the amplification effect of the subsequent laser-scattering PUF, if an attacker wants to obtain information through replication and cloning, he not only needs to clone the distribution of the disordered scattering medium in the laser-scattering PUF, but also needs to clone the uneven distribution of the particles on the VO 2 thin film, which makes the workload huge. At the same time, since the laser will interact with each particle on the thin film, the attacker also needs to restore the physical properties (such as refractive index, etc.) of each particle, which is almost impossible for the attacker to do. Therefore, the VO 2 thin film makes it more difficult to physically clone.

[0073] Figure 5 is the statistical chart of the size distribution of the surface particles in the SEM image of the VO 2 thin film. The size of the VO 2 particles shows a sharp distribution, with the particle size ranging from 63 to 224 nm and an average size of 109 nm.

[0074] (2) VO2 Preparation of VO / R-PUF

[0075] VO 2 VO / R-PUF is essentially a combination of a traditional laser-scattering PUF (disordered scattering medium) and the prepared VO 2 thin film. In this example, the writing surface of a glass slide produced by Unimark Corporation in the United States is selected as the traditional laser-scattering PUF. Its writing surface is composed of a disordered scattering medium, which has good light scattering effect and can be used as an ideal laser-scattering PUF. The VO 2 thin film prepared by magnetron sputtering is directly combined with the traditional laser-scattering PUF (composed of a disordered scattering medium) to obtain VO 2 / R-PUF.

[0076] Step 2. Complete the speckle reconstruction of VO 2 / R-PUF.

[0077] In this example, the temperature of VO 2 / R-PUF is changed to induce the IMT phase transition of the VO 2 thin film layer, and the speckle information during the heating and cooling processes (25°C, 35°C, 45°C, 55°C, 65°C, 68°C, 75°C) is captured. The VO 2 thin film after phase transition will modulate the wavefront of the infrared laser, and the changed wavefront information will be amplified by the laser-scattering PUF (disordered scattering medium), thus obtaining another completely different speckle.

[0078] VO 2 / R-PUF sample and the heater are placed about 20 cm behind the laser emission point, and the CCD camera is fixed about 20 cm behind the sample to receive the speckle information. The 1550 nm infrared laser emitted by the laser is guided to a suitable position through a single-mode optical fiber. The VO 2 / R-PUF is fixed on the back of the heater. The middle of the heating table is hollowed out so that the laser can pass through the heating table and reach the VO 2 / R-PUF smoothly. The temperature of the heating table is adjusted through an intelligent temperature control platform, and the speckle information scattered by the infrared laser by the VO 2 / R-PUF is collected by the CCD camera. It should be noted that the laser emission point, the center point of the VO 2 / R-PUF and the CCD camera should be at the same height. The VO 2 / R-PUF is irradiated by a 1550 nm infrared laser with a power density of 0.318 W / cm 2 , but such a power density will not cause photoinduced phase transition of the VO 2 thin film.

[0079] The process of speckle acquisition is as follows: For each sample (containing VO 2 thin film of VO 2 / R-PUF), the same acquisition method is adopted, and speckle information is collected at 25°C, 35°C, 45°C, 55°C, 65°C, 68°C, and 75°C respectively. During this process, other experimental parameters remain unchanged, and only the temperature of the sample is changed in situ. It should be noted that after each set temperature is reached, it is necessary to keep the temperature for 2 minutes before collecting the speckles to ensure that the actual temperature of the sample is the same as the set temperature, thereby reducing experimental errors. There are two stages of heating and cooling in the experimental process. During the heating process, the collection is carried out sequentially upward from 25°C, and during the cooling process, the collection is carried out sequentially downward from 75°C.

[0080] Figures 6A - 6D For laser-scattering PUF (without VO 2 thin film) and VO 2 / R-PUF assembled with a VO 2 thin film with a thickness of 396 nm, the speckle patterns collected at 25°C and 75°C are shown respectively.

[0081] From Figure 6A it can be seen that the laser speckles are light and dark spots, showing a disordered and irregular distribution, indicating that the 1550-nm laser is well scattered by the disordered scattering medium in the laser-scattering PUF. Comparing Figure 6B , when the temperature of the laser-scattering PUF rises from 25°C to 75°C, the speckles are almost exactly the same and no change occurs. As shown within the solid-line ellipse in the figure, almost all the characteristic points remain unchanged. This shows that a pure laser-scattering PUF can only form laser speckles, and temperature change cannot reconstruct the speckles. At the same time Figure 6A and Figure 6B also prove the stability of the speckle reading system. Since the laser is very sensitive to the position of the PUF, a slight change in position will cause a change in the speckles.

[0082] Figure 6C and Figure 6D are the speckle patterns of VO 2 / R-PUF at 25°C and 75°C respectively. It can be seen that the laser is still strongly scattered, and the speckles at 75°C are almost completely reconstructed compared with those at 25°C. As shown in the dotted-line part of the figure, at 25°C, this part is black and white and relatively evenly distributed, while when the temperature is 75°C, the white spots in this part are significantly increased, which is completely different from the speckles before the VO 2 phase change.

[0083] To prove that the reconstruction of the speckles is due to VO 2Caused by the phase change of the thin film and more clearly indicating the degree of speckle reconstruction, the Hamming distance is used to measure the difference between two strings, and the similarity is used to measure the degree of difference between two speckle patterns.

[0084] For laser-scattering PUF (disordered scattering medium) and VO 2 / R-PUF, speckle patterns were collected at 25 °C, 35 °C, 45 °C, 55 °C, 65 °C, 68 °C, and 75 °C respectively. The speckles at 35 °C, 45 °C, 55 °C, 65 °C, 68 °C, and 75 °C were respectively compared with the speckles at 25 °C. The corresponding Hamming distance results are as Figure 7A shown ( Figure 7A the curve pointed by the symbol A1 in 2 represents the Hamming distance corresponding to 396 nm VO 2 / R-PUF, and the curve pointed by the symbol B1 represents the Hamming distance corresponding to laser-scattering PUF). The results show that laser-scattering PUF exhibits a lower Hamming distance value at all temperature points, which means that the change in temperature does not cause changes in the speckles. For VO 2 / R-PUF, when the temperature is below 68 °C, the Hamming distance value is small and changes relatively smoothly. When the temperature reaches 75 °C, the Hamming distance value rapidly increases from the original 0.251 to 0.418, far higher than the pre-set threshold of 0.3, indicating that the speckles of VO 2 / R-PUF have almost completely changed at 75 °C (compared with the speckles at 25 °C). This is because the phase transition temperature of the VO 2 thin film is about 68 °C, and the speckles are relatively thoroughly reconstructed at 75 °C. The corresponding similarity results are as Figure 7B shown ( Figure 7B the curve pointed by the symbol A1 in 2 represents the similarity corresponding to 396 nm VO 2 / R-PUF, and the curve pointed by the symbol B1 represents the similarity corresponding to laser-scattering PUF). The results show that the normalized similarity exhibits the same results as the Hamming distance, that is, laser-scattering PUF exhibits a relatively high similarity value at all temperatures, about 0.9. For VO 2 / R-PUF, when the temperature is below 68 °C, the similarity value is large and changes smoothly (both higher than 0.8). When the temperature reaches 75 °C, the similarity value rapidly drops to about 0.15, as Figure 7B indicated by the arrow in Figure 7B . The sudden decrease in similarity also indicates the mutability of speckle reconstruction, which is consistent with the mutability of the phase change of the VO 2 thin film. The similarity heat map of the speckles of VO 2 / R-PUF compared with each other at different temperatures is as Figure 7CAs shown, the comparison results show that the speckles at 75 °C have low similarity values with the speckles at other temperatures, while the speckle similarity between other temperatures is relatively high, indicating that the speckle reconstruction occurs due to VO 2 The film undergoes a complete phase change at 75 °C. Thus, VO 2 The reconstruction of laser speckles caused by the phase change of VO nanocrystals is further proven.

[0085] Step 3. Key processing of the speckles.

[0086] To better measure the reconstruction of the speckles, we perform the following key processing on the speckles and propose a method to double the coding capacity. First, obtain the original speckle patterns of the same VO 2 / R-PUF at 25 °C and 75 °C, then convert them into binary images (which only contain two types of pixel points, black and white, and each type of pixel point accounts for about 50% of the total number of pixel points), and finally convert the binary images into binary codes, where black pixel points are defined as "0" and white pixel points are defined as "1". In this way, the keys K i (L) and K i (H) at 25 °C and 75 °C are obtained respectively. These two keys are completely different, but they are from the same VO 2 / R-PUF (due to the speckle reconstruction caused by the phase change of the VO 2 film). Therefore, these two keys can be combined to form a new key K i , which enables the VO 2 / R-PUF to contain twice the original coding information, making it more effective in resisting attacks by attackers.

[0087] In this example, K i (L) and K i (H) each contain 327,680 bits, so there are 2 327680 coding possibilities respectively. K i doubles from 327,680 bits to 655,360 bits, and there are 2 655360 coding possibilities. Therefore, a simple doubling of the coding quantity can increase the coding possibilities by 2 327680 times, greatly improving anti-counterfeiting and information security. This makes it almost impossible for attackers to break through the defense even after sufficient attempts. In fact, the number of bits of the binary string can be further increased by improving the resolution of the CCD camera. It should be noted that the string with double coding information in this example does not require increasing the volume of the VO 2 / R-PUF, but only requires the VO 2 film to undergo a phase change.

[0088] Step4. Complete the VO 2 User authentication of / R-PUF.

[0089] VO 2 The registration process of the key pair of / R-PUF and the user authentication process are as follows: In an absolutely secure environment, the manufacturer captures the laser speckle patterns generated by VO 2 / R-PUF at 25°C and 75°C respectively, and transforms the original speckle patterns into binary codes K i (L) and K i (H). Finally, K i formed by K i (L) and K i (H) is stored in the database. After all the / R-PUF key pairs are registered, the user is assigned the corresponding VO 2 / R-PUF. When the user needs to perform identity authentication, he only needs to put the R-PUF x into the authentication device, and the device will automatically capture the speckles and transform them into binary strings K x , and at the same time compare K x with K i . When the Hamming distance between (K x , K i ) is less than the set threshold T, the authentication is successful.

[0090] A 27-time authentication is as Figure 8 shown. Among these 27 speckle patterns, only one is obtained from the same R-PUF. When the threshold is set to 0.3, the authentication accuracy rate is 100%. The corresponding Hamming distance obtained from the correct speckle is 0.244, and the corresponding Hamming distances obtained from the incorrect speckles are all around 0.5.

[0091] The stability of PUF authentication has always been the focus of PUF research. Repeatedly heat the VO 2 / R-PUF, and collect the speckles at 25°C and 75°C during each heating process. The speckles under different cycle numbers are compared with the speckles collected for the first time to obtain the Hamming distance, as Figure 9 shown. The results show that as the number of heating times increases, the Hamming distance remains at a relatively low value, all lower than the threshold 0.3, and there is no obvious increasing trend, indicating that the stability of VO 2 / R-PUF speckle reading is not affected by the number of heating times and has excellent repeatability. This benefits from the stable reversible phase change characteristics of the VO 2 film.

[0092] In addition, during the heating and cooling processes, the reconstruction of the laser speckles shows the characteristics of a hysteresis curve. As Figure 10AThe hysteresis curve of the shown similarity has a hysteresis temperature width ( Figure 10A In Figure 10A , the curve pointed by symbol c represents the similarity curve of the cooling process, and the curve pointed by symbol h represents the similarity curve of the heating process), indicating that the temperature points at which speckle reconstruction occurs are different during the heating and cooling processes, which is also consistent with the 2 change in the infrared transmittance of the VO thin film phase transition Figure 10B , which further proves that the reconstruction of laser speckles is due to the 2 phase transition of the VO thin film. Figure 10C For the similarity hot spot map of VO 2 / R-PUF during the cooling process, it can be seen that the dark area becomes significantly wider. The speckles at temperatures above 65 °C and other temperatures have lower Hamming distance values, while the speckles between temperatures above 65 °C show higher similarity, indicating that the speckles at temperatures above 65 °C are in a reconstructed state during the cooling process. This further demonstrates the hysteresis phenomenon of speckle reconstruction during the cooling process, fully indicating that the 2 phase transition of the VO thin film leads to the reconstruction of laser speckles. The reason for the hysteresis phenomenon of speckle reconstruction is that there are changes in volume and enthalpy during the 2 phase transition, there is absorption and release of latent heat, and nucleation and growth are required during the phase transition, so a certain degree of supercooling is needed, resulting in different phase transition temperatures of the 2 VO thin film during the heating and cooling processes.

[0093] Therefore, based on this hysteresis phenomenon of speckle reconstruction, it provides a new dimension for describing the "challenge - response" of VO 2 / R-PUF in addition to "laser - speckle". During the identity authentication process, the user not only needs to meet the requirement of matching the speckle Hamming distance, but also conforms to the corresponding characteristics of the similarity hysteresis curve, which effectively prevents the attack method of forging speckles.

[0094] In this example, VO 2 thin film is prepared by RF magnetron sputtering to obtain VO 2 / R-PUF. By using the reversible phase transition of the VO 2 thin film to change the refractive index to regulate the optical speckles of the traditional laser scattering type PUF, the speckles are reconstructed and then the challenge - response behavior is regulated, improving the coding ability of the PUF, and its coding ability is more than twice that of the traditional PUF. At the same time, the temperature hysteresis characteristic of the 2 VO phase transition provides a new encryption dimension for VO 2 / R-PUF, once again increasing the difficulty for counterfeiters to crack the password information. The same volume can carry more information, which has important significance for the security of anti-counterfeiting labels. In addition, good reproducibility makes VO 2The / R-PUF can be used for subsequent repetitive system authentication.

[0095] Example 2

[0096] In this example, two VO thin films with different thicknesses were prepared to demonstrate the influence of VO thin film thickness on the degree of laser speckle reconstruction. Specifically, metallic vanadium was used as the target, O was the reactive gas, Ar was the working gas, and VO thin films were prepared by RF magnetron sputtering. By controlling the sputtering time to be 50 min and 30 min respectively, VO thin films with thicknesses of 396 nm and 194 nm were prepared respectively. 2 thin films, for demonstrating the 2 influence of VO thin film thickness on the laser speckle reconstruction degree. Specifically, metallic vanadium was used as the target, O 2 as the reactive gas, Ar as the working gas, and VO 2 thin films were prepared by RF magnetron sputtering. By controlling the sputtering time to be 50 min and 30 min respectively, VO 2 thin films with thicknesses of 396 nm and 194 nm were prepared respectively.

[0097] Figures 11A - 11C Figures for the cross-section, surface SEM, and corresponding surface particle statistical distribution of the 194-nm-thick VO 2 thin film. From Figure 11A , Figure 11B and Figure 4 it can be seen that the thicknesses of the two VO 2 thin films are 194 nm and 396 nm respectively, and they are composed of fine VO 2 particles, and the surface is rough and uneven. The corresponding particle size statistical distribution of the 194-nm-thick VO 2 thin film is as shown in Figure 11C . The particle size of the 194-nm-thick film is distributed between 47 nm and 240 nm, with an average value of 101 nm; while the particle size of the 396-nm-thick film is distributed between 63 nm and 224 nm, with an average size of 109 nm (as shown in Figure 5 ). The thicker film has a larger average particle size because a longer sputtering time leads to further growth of the crystal grains. The difference in their average particle sizes is 8 nm, and this difference will not cause a large difference in the scattering and modulation of 1550-nm laser. From the surface, the films of both thicknesses are uneven and have non-uniform particle sizes, and the surface morphologies are not very different, which can be used to consider the influence of VO 2 thin film thickness on laser speckle reconstruction.

[0098] The above-prepared VO 2 thin films with different thicknesses were combined with a laser-scattering type PUF (disordered scattering medium), and the speckles at different temperatures were collected and compared in the manner of Example 1 to explore the influence of VO 2 thin film thickness on the degree of speckle reconstruction. The speckle information read by the speckle reading system shows that the 194-nm VO 2The change in speckle before and after the phase transition of VO / R-PUF is relatively small, and the characteristics of most regions remain the same, with only minor changes in some regions. For the 396nm VO 2 / R-PUF, it can be directly seen that the speckle has undergone obvious reconstruction, and the speckle distribution in most regions has changed. The above results indicate that the thicker the VO 2 film, the greater the degree of speckle reconstruction. The reason for this phenomenon is that the thickness of the thinner VO 2 film in the laser propagation direction is quite different from the wavelength of the laser, and the modulation effect of the phase transition on the laser is not obvious, resulting in insignificant speckle reconstruction. The 396nm thick film is about 1 / 4 of the 1550nm wavelength, and the modulation of the laser is relatively obvious. It should be noted that the film thickness should not be too thick, otherwise the speckle signal will be too weak to collect information.

[0099] To more intuitively represent the degree of speckle reconstruction, we use the Hamming distance and similarity to measure the speckle reconstruction of the same VO 2 / R-PUF at different temperatures. Figure 12A Schematic diagram of the Hamming distance curve for VO 2 / R-PUF with different thicknesses; Figure 12B Schematic diagram of the similarity curve for VO 2 / R-PUF with different thicknesses; Figure 12C Schematic diagram of the similarity hysteresis curve for 194nm VO 2 / R-PUF. Among them, Figure 12A the curve pointed to by the symbol A2 represents the Hamming distance change curve corresponding to 194nm VO 2 / R-PUF, and the curve pointed to by the symbol B2 represents the Hamming distance change curve corresponding to 396nm VO 2 / R-PUF; Figure 12B the curve pointed to by the symbol A2 represents the similarity change curve corresponding to 194nm VO 2 / R-PUF, and the curve pointed to by the symbol B2 represents the similarity change curve corresponding to 396nm VO 2 / R-PUF; Figure 12C the curve pointed to by the symbol c in represents the similarity curve of 194nm VO2 / R-PUF during the cooling process, and the curve pointed to by the symbol h represents the similarity curve of 194nm VO2 / R-PUF during the heating process.

[0100] Figure 12A The Hamming distance results in show that 194nm VO 2 / R-PUF and 396nm VO 2The / R-PUF maintains a relatively low Hamming distance value when the temperature is below 68 °C. As the temperature increases, the Hamming distance value increases slowly (due to the thermal vibration of the device). When the temperature reaches 75 °C, the Hamming distance values of both increase significantly, indicating that the phase change of the VO 2 thin film causes the reconstruction of the laser speckle. It should be noted that the 194 nm VO 2 / R-PUF has a very small Hamming distance value even when the VO 2 thin film has completely undergone a phase change at 75 °C, only about 0.25, indicating that the thinner VO 2 / R-PUF causes a very small degree of speckle reconstruction. For the thicker 396 nm VO 2 / R-PUF, the Hamming distance value at 75 °C is 0.418, which has far exceeded the threshold of 0.3, indicating that the laser speckle has undergone obvious reconstruction.

[0101] The similarity shows the same pattern as the Hamming distance, as Figure 12B shown. At 75 °C, the similarity values of different thicknesses of VO 2 / R-PUF all decrease significantly. The decrease of the 396 nm VO 2 / R-PUF is more obvious, and the degree of speckle reconstruction is large. Therefore, it can be seen that the thickness of the VO 2 thin film affects the degree of laser speckle reconstruction. The thicker the thin film, the more obvious the speckle reconstruction.

[0102] Figure 12C This is the similarity hysteresis curve of the 194 nm VO 2 / R-PUF. Compared with the similarity hysteresis curve of the 396 nm VO 2 / R-PUF (as Figure 10A shown), both show the characteristics of the hysteresis curve of the VO 2 characteristics, indicating that the phase change of the VO 2 thin film does cause the reconstruction of the speckle. However, the hysteresis curve characteristics of the 396 nm VO 2 / R-PUF are more obvious, further indicating that the thicker VO 2 thin film will cause a greater degree of speckle reconstruction.

[0103] Therefore, the above experiments prove that the film thickness (i.e., increasing the film thickness) will increase the degree of laser speckle reconstruction. The thicker the VO 2 thin film, the more obvious the speckle reconstruction.

[0104] Example 3

[0105] In this example, the one-step method and the two-step method are used to regulate the surface morphology of the VO 2 thin film to demonstrate the VO 2Effect of the surface morphology of the thin film on the degree of laser speckle reconstruction. The one-step method is as follows: directly prepare VO thin film by one-step using the RF magnetron sputtering method. 2 The two-step method is as follows: first obtain low-valent vanadium oxide by adjusting the ratio of oxygen to argon, and then prepare VO thin films with different surface morphologies through heat treatment in a tube furnace. 2 The heat treatment in the tube furnace is as follows: introduce N₂ at a flow rate of 50 ml / min 2 to exhaust for five minutes, then heat the tube furnace to 512 °C at a heating rate of 8 °C / min for heat treatment. During the heat treatment, the N₂ gas flow rate is adjusted to 10 ml / min, keep the temperature for 70 min, and finally cool with the furnace. Open the furnace chamber after the temperature is lower than 100 °C to prepare VO thin films with different surface morphologies. The set parameters of the tube furnace are shown in Table 2. 2 2

[0106] Table 2 Specific process parameters for tube furnace annealing

[0107]

[0108] Figures 13A - 13C The VO thin film obtained by the two-step preparation method 2 SEM images of the cross-section and surface and the corresponding statistical distribution diagram of surface particle sizes. It can be seen that the thickness of the thin film prepared by the one-step method is 396 nm. From Figure 4 it can be seen that the thickness of the thin film prepared by the two-step method is 394 nm. The thicknesses of the thin films prepared by the two methods are basically the same, and the basically the same thickness can eliminate the influence of thickness on the degree of laser speckle reconstruction. Comparing the surface SEM images of the two thin films (i.e., Figure 13A and Figure 13B ) shows that the surface morphologies of the VO thin films obtained by the two methods are very different. The surface of the thin film prepared by the one-step method is uneven, and the particle size distribution is also very uneven. While the surface of the VO thin film prepared by the two-step method Figure 13B and Figure 4 is relatively flat, and the particle sizes are relatively uniform. 2 2 Figure 13C is the statistical distribution diagram of the surface particle sizes of the two-step method thin film. The particle sizes of the thin film prepared by the two-step method are distributed from 34 nm to 144 nm, and the average size is 81 nm; while the particle sizes of the thin film prepared by the one-step method are distributed from 63 nm to 224 nm, and the average size is 109 nm (as shown in Figure 5 ). Obviously, the average particle size of the VO thin film prepared by the two-step method 2 is smaller, and the difference between the two is about 28 nm. The different surface morphologies of the thin films are because the one-step method directly prepares VO thin film by using RF magnetron sputtering 2 ​​​​For the thin film, after subsequent heat treatment in the two-step method, grain recrystallization and growth occur, resulting in obvious differences in the surface morphology and particle size of the thin film.

[0109] Combine the VO thin films with different surface morphologies prepared above with laser scattering type PUF (disordered scattering medium), collect speckles at different temperatures in the manner of Example 1 and compare them to explore the influence of the VO thin film with different surface morphologies on the speckle reconstruction degree. The speckle information read by the speckle reading system shows that: the speckles of VO / R-PUF with different surface morphologies have all been reconstructed after phase change. For the one-step method VO thin film with more uneven particle distribution, more uneven and bumpy surface, and larger particle size, the speckle reconstruction of VO / R-PUF is more obvious, while for the two-step method VO thin film with concentrated particle distribution, relatively flat surface morphology, and smaller particle size, the degree of speckle reconstruction is smaller, and some characteristics before reconstruction are still retained in some areas. From the above results, it can be preliminarily judged that the more uneven and bumpy the VO thin film is, and the larger the particles are, the more obvious the reconstruction effect of the laser speckle is. 2 Combine the VO thin films with different surface morphologies prepared above with laser scattering type PUF (disordered scattering medium), collect speckles at different temperatures in the manner of Example 1 and compare them to explore the influence of the VO thin film with different surface morphologies on the speckle reconstruction degree. 2 The speckle information read by the speckle reading system shows that: the speckles of VO / R-PUF with different surface morphologies have all been reconstructed after phase change. 2 / R-PUF have all been reconstructed after phase change. 2 For the one-step method VO thin film with more uneven particle distribution, more uneven and bumpy surface, and larger particle size, 2 the speckle reconstruction of VO / R-PUF is more obvious, while for the two-step method VO thin film with concentrated particle distribution, relatively flat surface morphology, and smaller particle size, 2 the degree of speckle reconstruction is smaller, and some characteristics before reconstruction are still retained in some areas. From the above results, it can be preliminarily judged that the more uneven and bumpy the VO thin film is, and the larger the particles are, the more obvious the reconstruction effect of the laser speckle is. 2 For the one-step method VO thin film with more uneven particle distribution, more uneven and bumpy surface, and larger particle size, the speckle reconstruction of VO / R-PUF is more obvious, while for the two-step method VO thin film with concentrated particle distribution, relatively flat surface morphology, and smaller particle size, the degree of speckle reconstruction is smaller, and some characteristics before reconstruction are still retained in some areas. From the above results, it can be preliminarily judged that the more uneven and bumpy the VO thin film is, and the larger the particles are, the more obvious the reconstruction effect of the laser speckle is.

[0110] Figure 14A Shows the schematic diagram of the Hamming distance curve of VO / R-PUF with different surface morphologies; 2 Shows the schematic diagram of the Hamming distance curve of VO / R-PUF with different surface morphologies; Figure 14B Shows the schematic diagram of the similarity curve of VO / R-PUF with different surface morphologies; 2 Shows the schematic diagram of the similarity curve of VO / R-PUF with different surface morphologies; Figure 14C The schematic diagram of the similarity hysteresis curve of 394nm VO / R-PUF prepared by the two-step method. 2 The schematic diagram of the similarity hysteresis curve of 394nm VO / R-PUF prepared by the two-step method. Figure 14A The curve pointed by the symbol A3 in shows the Hamming distance change curve corresponding to the one-step method VO / R-PUF, and the curve pointed by the symbol B3 shows the Hamming distance change curve corresponding to the two-step method VO / R-PUF; 2 The curve pointed by the symbol A3 in shows the Hamming distance change curve corresponding to the one-step method VO / R-PUF, and the curve pointed by the symbol B3 shows the Hamming distance change curve corresponding to the two-step method VO / R-PUF; 2 The curve pointed by the symbol A3 in shows the Hamming distance change curve corresponding to the one-step method VO / R-PUF, and the curve pointed by the symbol B3 shows the Hamming distance change curve corresponding to the two-step method VO / R-PUF; Figure 14B The curve pointed by the symbol A3 in shows the similarity change curve corresponding to the one-step method VO / R-PUF, and the curve pointed by the symbol B3 shows the similarity change curve corresponding to the two-step method VO / R-PUF; 2 The curve pointed by the symbol A3 in shows the similarity change curve corresponding to the one-step method VO / R-PUF, and the curve pointed by the symbol B3 shows the similarity change curve corresponding to the two-step method VO / R-PUF; 2 The curve pointed by the symbol A3 in shows the similarity change curve corresponding to the one-step method VO / R-PUF, and the curve pointed by the symbol B3 shows the similarity change curve corresponding to the two-step method VO / R-PUF; Figure 14C The curve pointed by the symbol c in shows the similarity curve of 394nm VO2 / R-PUF prepared by the two-step method during the cooling process, and the curve pointed by the symbol h shows the similarity curve of 394nm VO2 / R-PUF prepared by the two-step method during the heating process.

[0111] Figure 14A For the Hamming distance values between the one-step and two-step VO 2 / R-PUF speckles (used to quantitatively characterize the speckle reconstruction degree), it can be seen that the VO2 / R-PUF prepared by the one-step method with an uneven surface and larger particle size has a larger Hamming distance value at a temperature of 75 °C, about 0.418, while the VO 2 / R-PUF prepared by the two-step method with a relatively flat surface and smaller particle size has a Hamming distance value of 0.284 at a temperature of 75 °C. It is worth mentioning that the Hamming distance values of both increase suddenly from 68 °C to 75 °C, indicating that the reconstruction of the speckles is caused by the phase change of VO 2 , and the change trends of the Hamming distance value curves of the two are also similar. The speckle similarity value curve is as Figure 14B shown. For the one-step and two-step VO 2 / R-PUF, the similarity values decrease rapidly at 75 °C, being 0.154 and 0.687 respectively. Obviously, the decrease amplitude of the one-step method is greater, indicating that the reconstruction of the speckles is more obvious. At the same time, the similarity hysteresis curve of the 394nm VO 2 / R-PUF prepared by the two-step method is as Figure 14C shown. Compared with the similarity hysteresis curve of the 396nm VO 2 / R-PUF prepared by the one-step method (as Figure 10A shown), the hysteresis curve of the one-step VO 2 / R-PUF speckles is more obvious, indicating that the reconstruction degree of its speckles is greater. The above results quantitatively illustrate the relationship between the speckle reconstruction degree of VO 2 / R-PUF and the surface morphology of the VO 2 thin film, that is, the more uneven the surface and the larger the particle size, the greater the speckle reconstruction degree.

[0112] Therefore, the above experiments prove that rough thin films (i.e., increasing the surface roughness) will increase the reconstruction degree of laser speckles. The rougher and more uneven the thin film surface and the larger the particles forming the thin film, the more obvious the speckle reconstruction caused by the phase change.

[0113] In summary, the beneficial effects of the present invention include at least one of the following:

[0114] (1) The present invention proposes a reconfigurable laser scattering optical PUF, which can solve the problems of fixed challenge-response characteristics and limited coding capacity of traditional laser scattering PUFs;

[0115] (2) The anti-counterfeiting authentication label based on the reconfigurable laser scattering optical PUF formed by the present invention has the characteristics of good repeatability, high coding capacity, large challenge-response regulation freedom, and high security;

[0116] (3) The anti-counterfeiting authentication method based on the reconfigurable laser scattering optical PUF formed by the present invention completes user identity authentication from two encryption dimensions: "laser-speckle" reconstruction and similarity lag curve features. This effectively prevents attacks by forging speckles and increases the difficulty for counterfeiters to crack password information.

[0117] Although the present invention has been described above in connection with exemplary embodiments and the accompanying drawings, those of ordinary skill in the art should understand that various modifications can be made to the above embodiments without departing from the spirit and scope of the claims.

Claims

1. An anti-counterfeiting label based on a reconfigurable laser scattering optical PUF, characterized in that, the anti-counterfeiting label includes a reversible phase change layer and a disordered scattering medium layer. The reversible phase change layer is attached to the upper surface of the disordered scattering medium layer, and the thickness of the reversible phase change layer is 50 nm to 1000 nm, and the average particle size is 20 nm to 500 nm; the reversible phase change layer refers to a thin film layer formed by a reversible phase change material with reversible insulator-metal phase change characteristics; during authentication, the reversible phase change layer is induced to undergo a reversible phase change to complete the speckle reconstruction of the anti-counterfeiting label; the disordered scattering medium layer is composed of a high refractive index material.

2. The anti-counterfeiting label based on a reconfigurable laser scattering optical PUF according to claim 1, characterized in that, The reversible phase change layer includes VO 2 and GST.

3. The anti-counterfeiting label based on a reconfigurable laser scattering optical PUF according to claim 1, characterized in that, the way for the reversible phase change layer to undergo a phase change is thermal stimulation, electrical stimulation, optical stimulation or strain stimulation.

4. The anti-counterfeiting label based on a reconfigurable laser scattering optical PUF according to claim 1, characterized in that, The disordered scattering medium layer is TiO 2 , ZrO 2 or ZnO.

5. The anti-counterfeiting label based on a reconfigurable laser scattering optical PUF according to claim 1, characterized in that, the thickness of the reversible phase change layer is 150 nm to 450 nm, and the average particle size is 200 nm to 500 nm.

6. The anti-counterfeiting label based on a reconfigurable laser scattering optical PUF according to claim 5, characterized in that, the Hamming distance of the reversible phase change layer before and after reconstruction can be between 0.4 and 0.

6.

7. An authentication method for an anti-counterfeiting label based on a reconfigurable laser scattering optical PUF, characterized in that, the authentication method includes: inducing the reversible phase change layer on the anti-counterfeiting label according to any one of claims 1 to 6 to undergo a reversible phase change to complete the speckle reconstruction of the anti-counterfeiting label, and obtaining the speckle pattern before reconstruction and the speckle pattern after reconstruction; Digitally process the speckle pattern before reconstructing the anti-counterfeiting label and the speckle pattern after reconstruction respectively to extract the key, and obtain the key K i (L) before reconstruction and the key K i (H) after reconstruction. Perform a Boolean operation on the key before reconstruction and the key after reconstruction to form the registration key K i , and store it in the database of the laser speckle reading device; Obtain the key K before reconstruction of the anti-counterfeiting label to be authenticated using a laser speckle reading device x (L) and the key K after reconstruction x (H), and perform a Boolean operation to form the key K to be authenticated x , calculate the key K to be authenticated x and the Hamming distance from the registered key K i . When the Hamming distance between (K x , K i ) is less than the preset threshold T, the user identity authentication is successful; otherwise, the user identity authentication fails.

8. The authentication method for an anti-counterfeiting label based on a reconfigurable laser scattering optical PUF according to claim 7, characterized in that, the preset threshold T is 0.1 to 0.

3.

9. The authentication method for an anti-counterfeiting label based on a reconfigurable laser scattering optical PUF according to claim 7, characterized in that, the authentication method further includes: judging whether the characteristics of the key similarity change curve of the anti-counterfeiting label to be authenticated under the stimulation condition match the characteristics of the key similarity change curve of the anti-counterfeiting label registered in the database. If so, the user identity authentication is successful; otherwise, the user identity authentication fails.

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