JP2013539874A - Method for manufacturing a product that embodies a physical replication difficulty function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a product embodying a physical duplication difficulty function (PUF).
The present invention is directed to a product that embodies the PUF. Disclosed is a method that relies on a material having one surface with “deterministic” asperities to produce such a product. This method further uses particles that are dimensioned to be trapped by surface irregularities. In general, this method allows particles (20) to be randomly deposited on the material surface (12) and trapped by their irregularities (14) to obtain a pattern that forms a PUF. The resulting PUF is easy to read because the general pattern and position of the particles are known. Only the loading level of the particles (of a given type) is random.
[Selection] Figure 1

Description

  The present invention relates generally to the field of physical replication difficulty functions as well as methods for producing products that embody such functions.

  Physical Unclonable Function (Physically Unclonable Function) (Physically Unclonable Function, also referred to as PUF for short) is a function embodied in a physical structure that evaluates It is easy, but difficult to fully characterize, see for example Non-Patent Document 1 for a good introduction This concept was already used in the early 90s, for example Patent Document 1 Typically, a structure that includes a PUF has random components that are introduced during the manufacture of the structure that cannot be fully controlled, and thus is physically associated with the structure that embodies the PUF. Applying a stimulus (challenge) fully predicts due to its random components It is impossible to do so (response), but this result is (ideally infinite) reproducible, so a given challenge and its response can be combined into a unique challenge − Response pairs are formed, for example, a cracked or rough surface can be challenged with incident light to produce a unique scattering pattern, two PUFs manufactured by essentially the same process Will have different challenge-response behavior, which is the result of complex interactions between the challenge and the random components of the structure. Therefore, a PUF is said to be difficult to replicate.

  You can rely on different sources of randomness. In that respect, it is possible to distinguish between a PUF in which randomness is introduced exogenously and a PUF that uses the intrinsic randomness of the physical system.

  For example, microelectronic semiconductor chips are characterized by intrinsic randomness inherent in detailed electronic characteristics due to small variations in their manufacturing process, for example, silicon PUFs are intrinsic random in wire and gate delays. Take advantage of fluctuations. The advantage is the possibility of scale reduction and IC integration. More problematic is the typical long-term drift and read reproducibility.

  Examples of PUFs that use extrinsic randomness are optical PUFs and coated PUFs. The optical PUF can be obtained, for example, from a transparent material doped with light scattering particles. When the material is illuminated, a random and unique scattering pattern is generated. For example, see Non-Patent Document 2.

  Coated PUFs are also known and can be constructed, for example, by filling the space defined by the comb structure with an opaque material randomly doped with dielectric particles in the upper layer of the IC. For example, see Non-Patent Document 3.

  In general, exogenous PUFs allow high reproducibility and easy reading, but are often difficult to incorporate markers and are limited in size scaling.

European Patent Application No. 058709 (A1) specification

Wikipedia <http: // en. wikipedia. org / wiki / Physically_unclonable_function> R. Pappu, B.I. Recht, J.M. Taylor, and N.A. Gershfeld, “Physical One-Way functions”, Science, September 2002, Vol. 297 (5589), p. 2026-2030 <http: // dx. doi. org / 10.1126 / science. 1074376> B. Skoric, S.M. Maubach, T .; Kevenaar and P.A. Tuyls, “Information-theoretic analysis of capacitive physical unclonable functions”, J. Am. Appl. Phys. July 2006, Vol. 100, No. 2, p. 024902 <http: // dx. doi. org / 10.1063 / 1.2209532> Malaquin et al., Langmuir, 2007, Vol. 23, p. 11513

  In each of the above cases, intrinsic or extrinsic randomness is utilized to generate a PUF with each unique challenge-response pair. Such functions are important for use in anti-counterfeiting and cryptographic applications, for example. Unfortunately, the randomness component of the PUF can drift or degrade over time.

  More generally, reading a PUF becomes difficult due to degradation or drift over time and / or certain inherent difficulties.

  In one embodiment, the present invention provides a method for manufacturing a product that embodies a physical replication difficulty function or PUF, the method comprising: a material having deterministic irregularities on one surface; Providing particles that can be trapped in the irregularities, and depositing the particles randomly on the surface to obtain a PUF and trapping in the irregularities.

In other embodiments, the method can include one or more of the following features.
The preparing step comprises preparing the particles as a colloidal suspension in a liquid, preferably water, and the step of randomly depositing the particles comprises applying the liquid to a surface having irregularities.
The surface irregularities, particles and liquid of the prepared material are selected such that the particles are subject to capillary forces at the surface, the characteristic dimensions of both particles and irregularities are preferably on the order of micrometers.
The step of depositing the particles randomly is to apply the liquid to the surface by using a lid to maintain the liquid layer against the uneven surface, whereby the liquid meniscus is on the surface And moving the lid or surface in accordance with the evaporation rate of the liquid at a specified meniscus level, wherein the liquid is preferably heated. Including.
The prepared liquid further comprises a surfactant that affects the contact angle formed by the meniscus at the surface.
The preparing step comprises preparing different types of particles, the different types of particles preferably having different respective colors;
-The step of preparing includes the step of preparing a material having a pre-processed surface irregularity.
The prepared deterministic surface irregularities form a 2D array.
The prepared deterministic surface irregularities form an array of open corners.
The prepared particles are each beads having a fluorescent dye, and the particles are preferably polystyrene beads.
The method of the present invention further comprises a preceding step of forming the prepolymer in a mold and polymerizing the prepolymer to form a material with surface irregularities, the material preferably being PDMS.
The method of the present invention further comprises the step of fixing the deposited particles;
-The surface of the material to be prepared has a set of unevenness, and the set of unevenness, when the unevenness where the particles are trapped in the set is illuminated, the particles are trapped there It is designed to produce a scattering pattern that is substantially different from the scattering pattern produced by no irregularities. The present invention, according to another aspect, is directed to a product embodying a PUF obtained according to an embodiment of the method according to the invention.

  According to a last aspect, the present invention is directed to a method for performing a challenge-response assessment of a product according to the invention, the method comprising the steps of preparing a product according to the invention and determining the surface Stimulating the surface of the product with particles deposited on the theoretical irregularities to obtain a response and reading the response according to the deterministic irregularities.

  Products and methods embodying the present invention will now be described by way of non-limiting examples and with reference to the accompanying drawings.

1 is a schematic diagram of a method for manufacturing a product embodying a PUF in an embodiment of the present invention. FIG. 2 is a diagram of an experimental setup for performing both, for example, the method of FIG. 1 and the corresponding PUF challenge-response evaluation in an embodiment. 2 is a microscopic image of ˜1 μm polystyrene particles suspended in water and deposited on a PDMS surface, according to an embodiment. 2 is a bright field optical microscope image showing fluorescent polystyrene spheres deposited and trapped in a corner array, according to an embodiment. FIG. 5 is a gray scale negative of a fluorescence microscope image (channel overlay) obtained for the deposited polystyrene spheres of FIG. 4. It is the schematic which showed a mode that the challenge by incident light was applied to PUF obtained in embodiment, and the unique scattering pattern was produced | generated. FIG. 3 shows the steps of molding and polymerizing a prepolymer to form a material having a surface suitable for carrying out the method of FIG. 1 or FIG.

  As an introduction to the following description, we first focus on the general aspects of the present invention directed to products that embody PUFs. The method for producing such products relies firstly on materials having one surface with “deterministic” irregularities, ie irregularities determined due to preceding events or natural laws. To do. This method further uses particles configured to be trapped by surface irregularities. In general, this method allows particles to be randomly deposited on the material surface and trapped in the irregularities of the material surface so as to obtain a patterned material surface that forms the PUF. As can be seen, the resulting PUF is easier to read due to the (partial) knowledge of its surface, ie its deterministic aspect. For example, the general pattern and position of the particles can be known in advance, and only the packing level of the particles (of a given type) is random.

  An example of such a method is shown in FIG. First, the method includes providing a material 10 such as polydimethylsiloxane (PDMS) having one surface 12 having deterministic irregularities 14. Particles 20 such as polystyrene (PS) beads are further prepared, for example as a colloidal suspension. Such particles are selected such that they can be trapped in the aforementioned irregularities. Typically, their characteristic dimensions are less than or on the order of irregularities, as shown in the enlarged view in FIG. The particles are then randomly deposited on the surface 12 (S40) and trapped on some of the irregularities 14 on the surface 12 (S50). The resulting pattern of deposited particles forms the PUF. As mentioned above, this pattern is partially deterministic while the occupation probability by the particles retains a random component.

  As mentioned above, the particles are preferably prepared as a colloidal suspension in a liquid 30 such as water. Therefore, by applying a liquid to the surface (S20), it is possible to easily deposit particles randomly on the surface. The random dispersion of the particles in the liquid will ultimately ensure a random packing. A different form that is less practical than that may consist of mechanically distributing the particles into surface irregularities, for example by sputtering.

Preferably, the particles and liquid are selected such that the particles undergo capillary forces at the surface (denoted by F _{c in} FIG. 1) during deposition. In that regard, the characteristic dimensions of the particles and irregularities are typically on the order of micrometers. Therefore, the trapping of the particles in the irregularities can be assisted in part by capillary forces. In different forms, particles are trapped by their momentum. In other different forms, the respective conformation of the irregularities versus particles allows the particles to be trapped in the irregularities. The particles may actually be slightly larger than the irregularities, such as holes in the surface, provided that the particles are deformable and have sufficient momentum when they reach the irregularities, or The condition is that a sufficient force, for example a capillary force, is applied to the particles. The latter scenario is preferred, and hereinafter the latter scenario is assumed.

  In that regard, one way to achieve a capillary assisted deposition process is to apply the liquid 30 to the surface 12 by using the lid 40 to maintain the liquid layer 30 against the surface. is there. A meniscus 32 is accordingly formed between the surface 12 and one end 41 of the lid 40. The meniscus is the interface between air and liquid, where the liquid attempts to evaporate at a rate determined by the experimental geometry and thermodynamic conditions (step S30), resulting in the meniscus retracting. As shown in the enlarged view in FIG. 1, the meniscus 32 exerts more pressure on the particles near the interface when retreating (see, for example, Non-Patent Document 4), thereby causing the particles to be uneven. Trap at.

  Interestingly, both the capillary forces and the confinement forces that occur once a particle is trapped are strong short-range forces. They therefore result in a highly accurate deposited particle pattern, at least in the situation as in FIG. Capillary force acts only for a short period of time, ie, as long as it corresponds to capillary breakup as the meniscus retracts, as shown in the enlarged view of FIG.

  Better performance can be further achieved by appropriately adjusting the contact angle of the meniscus at the surface, for example by selecting a convenient liquid and / or surfactant. A surfactant is a surfactant molecule. At low concentrations, surfactant molecules are likely to be present at the air / water interface, where they reduce surface tension. When CMC (critical micelle concentration) is reached, the surfactant begins to form further micelles. Surfactant molecules usually have a hydrophilic head group and a hydrophobic tail group (long alkyl chain). The hydrophilic head group can be cationic, anionic, or nonionic. Whether to use ionic (and its charge) or non-ionic surfactants may depend on the colloidal system. The surfactant is preferably selected so as not to cause aggregation and precipitation of the colloidal particles. In some cases, a mixture of surfactants is advantageous. Useful concentrations are mostly in the mM range, but can vary considerably. By using a surfactant, the contact angle can be adjusted to a smaller value, so that the meniscus protrusion on the surface is as large as possible and the corresponding force as shown. Can have a vertically downward component.

  The relative dimensions of the particles and irregularities, the concentration of the particles in the liquid, the nature of the particles and the liquid can be adjusted by a trial and error process. A suitable example is shown below.

  In accordance with this principle, the entire surface 12 can be patterned by moving the lid or surface according to the evaporation rate of the liquid at the level of the meniscus 32 (step S20). In that regard, FIG. 3 shows a microscopic image of particles deposited on the patterned PDMS surface. Here, the particles are ˜1 μm PS particles suspended in water. Particles 20 already deposited on the array 16 can be seen on the left side of the meniscus 32. On the right side, the particles are still suspended in the water 30.

  Note that this process can be aided by heating the liquid during operation to accelerate the process.

  The particles used are advantageously of different types, allowing different randomness axes that can be used later during the challenge step. For example, the particles can have different colors. Thus, a given color particle randomly fills the irregularities (the irregularities are not color selective).

FIG. 2 shows a capillary assisted particle assembly device that allows the method as described above to be performed. This instrument
A stepper motor 61 for driving the electric translation stage 62;
A heat exchanger 63 with a fluid input 63 ′ and an output 63 ″ for thermally assisting the process above the stage 62;
A Peltier element 64, ie a solid heat pump that transfers heat from one side of the device to the other, is further provided;
The material 10 to be patterned is placed on a Peltier element and a colloidal suspension 20, 30 is applied thereon by a lid 40 (ie just a confinement slide) as described with reference to FIG. And maintained. A guided slide holder (not shown) allows movement of the lid.
An optical microscope 65 for process monitoring and a camera 66 (for contact angle measurement) can be further provided.

In a particular embodiment, the PUF is fabricated by capillary depositing ˜1 μm fluorescent beads in a concavo-convex array 16 that is an open top corner 17 as shown in FIG. Similar to the crystal lattice, other types of arrays / concaves can be used for capillary deposition. A corner array is a square grid with a given spacing and pattern, for example, with a translation vector a,

It is. | A | can be further tuned to optimize subsequent scattering patterns (eg, to minimize crosstalk in reading). The colloid used in the capillary assembly contains a mixture of different (fluorescent) colored beads. The deposition of beads on the irregularities can be designed to obtain a high yield. However, there is no selectivity for the color of the beads. Thus, as a result of the deposition, different colored beads are randomly placed on the template as shown in FIG. The resulting bead array is difficult to replicate because the beads are too small to be able to “manually” place many in a time that can be accommodated.

  The challenge step is performed, for example, by UV / V illumination of a bead array, as shown in FIG. 6, with each bead responding by emitting its corresponding fluorescent color. Such characterization techniques are known per se, basically illuminating the patterned surface (step S100) to obtain a scatter pattern and collecting this scatter pattern with any suitable camera. (Step S110). The resulting pattern of colored spots is inherently difficult to replicate. Since the PUF has a known bead pattern and position, it can be easily read (step S120). In this case, only the bead color is random (assuming a fill probability of ˜1). By the way, since the position of the beads is determined through the template, a fixed structure such as an adjustment grid or alignment structure that supports automatic recognition (step 120) can be conveniently inserted into the challenge step. In other words, this “fixed structure” reflects the deterministic nature of the irregularities. More generally, the patterned surface of the product will be stimulated to obtain a unique response, which can then be read according to the challenge-response principle described above. In this case, reading the response can be facilitated by a partial knowledge of the surface, ie by its deterministic aspect. As described above, a fixed structure, such as an adjustment grid or alignment structure, can be advantageously used to support automatic recognition, thereby facilitating response interpretation. For example, a structure such as an alignment structure known in standard lithographic applications can be used. Miniaturized logos and codes (eg, field numbers, coordinates ...) are also possible. This is not possible, for example, with glass-based PUFs that rely on surface cracks. The challenge-response evaluation process, for example based on light scattering, is otherwise known per se.

  In a different form, the PUF is based on a pre-defined pattern such as an array and allows random deposition of beads on surfaces whose irregularities are less deterministic or more deterministic than the above example It is also possible to generate it. For example, surface characteristics (eg, default) can be determined to some extent, eg, statistically. However, in such cases, the challenge / response is probably more problematic. That is, at low bead density / concentration, the beads will produce a low response number (which requires a larger area and / or longer readout time), while at higher concentrations, the beads are close to each other. To make reading more difficult or even impossible (crosstalk). Thus, it is understood that a convenient surface should have reasonably predefined irregularities. Practical solutions result in a pre-determined deposited particle pattern (ie, an ordering parameter beyond just a random location of the trap site is provided), or a surface that provides a preferred site Rely on.

In carrying out embodiments of the present invention, the following advantages are generally sought.
The optical reading and scanning are essentially deterministic as opposed to statistical semiconductor related PUFs.
-It is assumed that deterioration over time is low, and there is essentially no drift as in the case of semiconductor-related PUFs.
Concomitantly, the reading can be enhanced by an error correction code that compresses to a smaller but reliably recoverable core bit.

  As an additional security feature, the assembly site pattern can be designed to form a characteristic diffraction pattern when illuminated with a light source, such as a laser. The assembly site can be designed, for example, in such a way that empty sites and filled sites generate different patterns. This can then be used to verify whether the beads have been assembled or not, simply that the fluorescent ink is producing a control image. Furthermore, the particles can be modified with quantum dots that emit a unique (fingerprint) spectrum.

  Preferably, fluorescent (red, green, and blue) polystyrene (PS) beads having a diameter of 1 μm are assembled by a capillary assembly, as described above, in corners of 2 μm in length, 1 μm in width, and 1 μm in height. . Although the corner pattern determines the position of the beads, the assembly process is not selective for the color of the beads. Therefore, a random color pattern can be generated.

  Corner patterns can be molded from structured silicon prototypes into polydimethylsiloxane (PDMS) or polymer resist (by nanoimprint lithography), as shown in FIG. For example, the PDMS prepolymer 10 'can be molded in the mold 5 prior to polymerization (S12) and removal (S14) (steps S10-S12). Such molding techniques are known per se. The polymerized shape provides a material suitable for the production of PUF as described above. In addition, the corner pattern can be formed using any material (polymer, glass, semiconductor, metal, metal oxide) that is easy to use for any type of lithography or molding method. Such materials can then be surface treated to achieve the wetting characteristics required for the capillary assembly.

After capillary deposition, ideally there is one PS bead in each corner as in FIG. The fluorescent colors 20 ′, 20 ″, 20 ′ ″ of the beads can be observed under a fluorescence microscope (as shown in FIG. 5 where a negative image of a grayscale image is drawn). Note that using three colors (RGB fluorescence) and only 100 assembly sites already results in an alternative assembly of 5.15378 × 10 ⁴⁷ (assuming one particle per site). . Instead, relying on a single type of particle, but adjusting the deposition process to reach a filling probability of 1/2 results in an alternative configuration of 1.26765 × 10 ³⁰ .

  The particle deposition step can be followed by any convenient step for immobilizing the particles (eg, applying an optically inert additional layer).

  Finally, the present invention is directed to a product embodying a PUF obtained by any of the methods described above.

  Although the invention has been described with reference to specific embodiments, those skilled in the art will recognize that various modifications can be made and equivalents can be substituted without departing from the scope of the invention. Will. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the scope thereof. Accordingly, the invention is not limited to the specific embodiments disclosed, but is intended to embrace all embodiments that fall within the scope of the claims. For example, the process can be adjusted dynamically (or spatially) by changing the composition over time or its concentration, or by adjusting the deterministic aspects of the surface 12 along the material. Can do. For example, several isolated irregularities can be provided, or the array can be varied along the surface (one square, the other rectangular, etc.). This can be useful to provide a specific tag or identifier. For example, a pre-treatment of a specific irregularity that is a signature of a given company, class of the given product, etc. can be performed.

5: Mold 10: Material 10 ′: Prepolymer 12: Surface 14: Concavity and convexity 15: Product embodying PUF 16: Array 17: Corner 20: Particle 30: Liquid 32: Meniscus 40: Lid 41: One end of lid 61: Stepper motor 62: Electric translation stage 63: Heat exchanger 63 ′: Fluid inlet 63 ″: Fluid outlet 64: Peltier element 65: Optical microscope 66: Camera Fc: Capillary force

Claims (15)

A method (S20-S40) for producing a product (15) that embodies a physical replication difficulty function or PUF, comprising:
Providing a material (10) having deterministic irregularities (14) on one surface (12) and particles (20) that can be trapped in said irregularities;
Depositing the particles randomly on the surface to obtain the PUF (S40) and trapping in the irregularities (14) (S50);
Including methods. The step of preparing comprises preparing the particles as a colloidal suspension in a liquid, preferably water;
The step of randomly depositing the particles includes the step of applying the liquid to the surface having the unevenness (S20).
The method of claim 1. The surface irregularities, the particles and the liquid of the material to be prepared are selected such that the particles receive a capillary force (F _c ) at the surface, and the characteristic dimensions of both the particles and the irregularities are preferably The method of claim 2, which is on the order of micrometers. The step of depositing the particles randomly;
Applying the liquid to the surface (12) by maintaining the liquid layer (30) against the irregular surface using a lid (40), whereby A liquid meniscus (32) is defined between the surface (12) and one end (41) of the lid;
Moving the lid or the surface according to an evaporation rate (S30) of the liquid at the defined meniscus level (S20), wherein the liquid is preferably heated. 3. The method according to 3.   The method of claim 4, wherein the prepared liquid further comprises a surfactant that affects a contact angle formed by the meniscus at the surface.   6. A method according to any one of claims 1 to 5, wherein the preparing step comprises preparing different types of particles, the different types of particles preferably having different respective colors. Method.   The method according to any one of claims 1 to 6, wherein the step of preparing includes the step of preparing a pre-treated material (10) having surface irregularities (S10-S14).   Method according to claim 7, wherein the prepared deterministic surface irregularities form a 2D array (16).   Method according to claim 8, wherein the prepared deterministic surface irregularities form an array (16) of open corners (17).   10. A method according to claims 1 to 9, wherein the prepared particles are beads (17) each containing a fluorescent dye, and the particles are preferably polystyrene beads.   The prepolymer (10 ′) is molded in the mold (5), the prepolymer is polymerized (S12) to form the material (10) having the surface irregularities, and the preceding steps (S10-S14) are further performed 11. A method according to any one of claims 1 to 10, comprising, wherein the material is preferably PDMS.   12. A method according to any one of claims 1 to 11, further comprising the step of fixing the deposited particles.   The surface of the material to be prepared has a concavo-convex set, and the concavo-convex set, when the concavo-convex with the particles trapped therein is illuminated, the particles in the ensemble are there. 13. A method according to any one of the preceding claims, wherein the method is designed to produce a scattering pattern that is substantially different from the scattering pattern produced by untrapped irregularities.   A product embodying a PUF obtained by the method according to any one of claims 1 to 13. A method for performing a challenge-response assessment of a product according to claim 14, comprising:
Preparing the product of claim 14;
Stimulating the surface of the product having particles deposited on the deterministic asperities of the surface (S100) to obtain a response (S110);
Reading the response according to the deterministic irregularities (S120);
Including methods.