JP2011158817A - Cipher recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cipher recording medium where two cipher images are formed on the same base material using a vision decoding type secret sharing method, and a troublesome operation such as exact overlapping of the two cipher images is not required in restoring an original image. <P>SOLUTION: A pixel of each cipher image by the vision decoding type secret sharing method is further divided, and an information cell 61 of the cipher image is formed of a diffraction grating a67 and diffraction grating b68 having different grating angles. Diffraction gratings of random grating angle or grating pitch are arranged in a margin cell 64. Thus, the two cipher images formed on the same base material are simultaneously, visually recognized only when irradiation is performed with two kinds of light sources having an irradiation angle suitable for the two kinds of diffraction gratings in the restoring, so that a masked image is decoded and becomes readable. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In the present invention, the recorded image is concealed so that it cannot be visually recognized in a normal state, and the concealed shape information is visualized under a light source of a specific condition at the time of restoration, and the original shape information can be read. The present invention relates to an encryption recording medium.

  In the normal state, there is a long-standing need to use information recorded in a concealed state when it is needed. For example, concealment seals and crimping postcards are familiar examples. These are one-time use (disposable) and are suitable for temporary use. On the other hand, while maintaining high secrecy when not in use, they can be restored by simple operation when used, and It is very difficult to meet the conflicting requirement of being reusable.

  There is a visual decryption type encryption technique called a visual decryption type secret sharing method as one of the techniques for the above requirements. This is done by processing the original image information into an image that cannot be visually recognized by dispersing it into a plurality of images (called shared images) composed of irregular patterns, and then superimposing the shared images. This technique restores the original image information to a visible state.

  For example, Patent Document 1 is a representative example of visual decryption encryption technology, and a technology related to the configuration and production of a recording medium that conceals information without using a concealment layer or the like using a visual decryption secret sharing method. Is disclosed.

  Various methods have been proposed for the visual decryption secret sharing method, the shared image generation means, and the like, and the principle and generation method are described in detail in Non-Patent Document 1, which is a pioneering paper. .

JP 2001-118122 A

M.Naor and A.Shamir, "Visual Cryptography", Proc. Of Eurocrypt'94 May 1994 As mentioned above, the visual decryption secret sharing method has the advantage of simplicity that can be restored by visual manual operation. However, on the other hand, since the original image is restored by superimposing a plurality of shared images, it is necessary to use the same number of media as the number of shared images, and in order to restore the original image, these multiple media are precisely superimposed. Operation is required.

  FIG. 1 is a diagram showing a process of encryption and restoration using the visual decryption secret sharing method. For example, as shown in FIG. 1, “T” of the restored image 13 is obtained from two shared images. In this case, the number of required media is 2, and a plurality of media are used. Moreover, as shown in FIG. 2, since the images are overlapped and visually observed, the overlapping surfaces of the two media need to be smooth so that they are in close contact with each other, and at least one of the media is a transparent sheet like the transparent medium a21. It is essential to be. Further, when two shared images are superimposed, there is a problem that it is difficult to distinguish between an image to be restored and a background because a white portion appears with a slight shift in overlap and a difference in density from the background becomes small.

  Therefore, the present invention can form two shared images on the same medium while using the visual decryption type secret sharing method, and has the trouble of superimposing the two shared images when restoring the original image. It is an object of the present invention to provide an encryption recording medium that does not require an operation.

The present invention for solving the above problems
A first encryption pattern and a second encryption pattern for generating an original image from an encryption image by a visual decryption secret sharing method are formed on a base material, and the first encryption pattern and the second encryption pattern are superimposed on each other. The cipher pattern is composed of a set of information cells and blank cells arranged in a small area obtained by dividing each pixel constituting the cipher image, the first information cell constituting the pixel of the first cipher pattern, In the encryption recording medium arranged so as not to overlap with the second information cells constituting the pixels of the second encryption pattern,
The first information cell and the second information cell are formed by diffraction gratings having different grating angles, and the blank cell is formed by a diffraction grating whose grating angle is an indefinite angle for each cell. Features.

  Furthermore, the blank cell may be formed by a diffraction grating having a grating angle different from that of an adjacent cell.

According to the present invention, a first cipher pattern and a second cipher pattern for generating an original image from a cipher image by a visual decryption secret sharing method are formed on a base material, and the first cipher pattern The pattern and the second cipher pattern are composed of a set of information cells and blank cells arranged in a small area obtained by dividing each pixel constituting the cipher image, and the first cipher pattern pixel constituting the first cipher pattern pixel. In the encryption recording medium arranged so that the information cells and the second information cells constituting the pixels of the second encryption pattern do not overlap each other,
The first information cell and the second information cell are formed by diffraction gratings having different grating angles, and the blank cell is formed by a diffraction grating having an indefinite grating pitch for each cell. And

  The blank cell may be formed of a diffraction grating having a grating pitch that is different from that of an adjacent cell.

  The grating angle of the diffraction grating forming the first information cell and the grating angle of the diffraction grating forming the second information cell are orthogonal to each other.

  According to the encryption recording medium of the present invention, since two share images can be formed on the same medium, the cost of the medium can be reduced, and an operation for superimposing the share images is eliminated. Further, since a transparent medium is not required and the sheet is not required to be a smooth sheet, there are no restrictions on the material and shape of the medium.

Conceptual diagram of visual decryption secret sharing method Diagram showing how the visual decryption secret sharing method is restored Diagram showing encryption pattern generation process Figure showing a restored image Diagram showing the process of generating a new cipher pattern Diagram showing observation state Diagram showing diffraction grating of blank cell The figure which shows the details of the restoration picture with new encryption pattern

  Hereinafter, the details of the encryption recording medium of the present invention will be described with reference to FIGS.

  FIG. 3 is a schematic diagram showing the encryption pattern generation process used for the encryption recording medium of the present invention in comparison with the encryption pattern generation process by the conventional visual decryption secret sharing method. FIG. 3A shows an encryption pattern generation process by a conventional visual decryption secret sharing method, and FIG. 3B shows an encryption pattern generation process according to the present invention, focusing on pixels forming each pattern. Explained. In the following description, the former is referred to as a share pattern and the latter is referred to as a new cipher pattern in order to distinguish the cipher pattern according to the conventional visual decryption secret sharing method from the cipher pattern according to the present invention.

  First, a share pattern based on the conventional visual decryption secret sharing method will be described.

  As shown in FIG. 3A, the share pattern based on the conventional visual decryption secret sharing method divides the pixels constituting the original image (pixel 30 of the original image) by an integer ratio (2 × 2 in the example). It is generated by dividing into areas 35 and assigning white or black to each divided area 35.

  The share pattern generated in this way is a pixel constituting the share image A and the share image B. That is, the share pattern a32a and the share pattern a33a are the pixels of the share image A, and the share pattern b32b and the share pattern b33b are the pixels of the share image B. Then, when the share image A and the share image B are overlapped and the original image is restored, a pixel representing “white” such that the overlay of the two patterns such as the share pattern a 32 a and the share pattern b 32 b is the restored pixel 32. Thus, the overlapping of the two patterns of the share pattern a33a and the share pattern b33b becomes a pixel representing “black” like the restoration pixel 33.

  Next, a new encryption pattern in the encryption recording medium of the present invention will be described.

  In the generation of the new cipher pattern of the present invention, as shown in FIG. 3B, first, the new divided pattern 41 (2 × 2 divided area 35 shown in FIG. 3A is further divided by an integer ratio. In the illustrated example, 6 × 6) is specified. A new cipher pattern a (a series pattern) and a new cipher pattern b (b series pattern) are generated by assigning white or black to the small areas thus divided (referred to as cells).

  The process of generating these two new encryption patterns will be described in detail later with reference to FIG.

  Further, in FIG. 3B, for the sake of understanding, different hatching is applied to the cells to which black of the a-series and b-series patterns are assigned, thereby distinguishing the new cipher pattern a and the new cipher pattern b. .

  Two kinds of patterns such as the new restoration pattern 42 or the new restoration pattern 43 are formed by combining the two kinds of new encryption patterns generated in this way. For example, when two patterns such as the new cipher pattern a42a and the new cipher pattern b42b are observed at the same time, it becomes a pixel (referred to as a “coarse” pixel) having a distribution of “concentrated” cells like the new cipher pattern 42. Similarly, when the two patterns of the new cipher pattern a43a and the new cipher pattern b43b are observed at the same time, pixels having a distribution of “distributed” cells like the new cipher pattern 43 (referred to as “dense” pixels). Become.

  FIG. 4 is a diagram showing the restored image based on the new encryption pattern generated in this way, compared with the restored image based on the conventional visual decryption secret sharing method, and FIG. 4 (A) shows the conventional visual decryption type. A restored image by the secret sharing method and FIG. 4B show a restored image by the encryption pattern of the present invention.

  FIGS. 4A and 4B show how the character part of “secret” can be distinguished from the background part and identified by combining two shared images.

  FIG. 4A showing a restored image by the conventional visual decryption secret sharing method observes an image that appears when two shared images are superimposed, and represents an irregular pattern representing “white” and “black”. The character part 36 and the background part 37 are distinguished from each other by the density difference of the fill pattern.

On the other hand, in the restored image using the encryption pattern of the present invention, the discrimination is made based on the difference in density between the pixel patterns of the character portion 46 and the background portion 47 as shown in FIG. That is, the state where the new restoration patterns 42 in FIG. 3B are gathered is visually recognized as a distribution of “coarse” pixels, and the collection of new restoration patterns 43 is visually recognized as a distribution of “dense” pixels.
<Generation of new cipher pattern>
FIG. 5 shows a state where a cell of a new encryption pattern used in the present invention is generated by dividing the original pixel.

  FIG. 5A is a diagram for explaining a template used for generating an encryption pattern in the present invention, and FIG. 5B is a diagram showing a process of generating a new encryption pattern using the template.

  The template 50 in FIG. 5A is obtained by assigning “1” or “2” to the new divided pattern 41 in a staggered pattern, and by applying the templates “1” and “2”, The pixel 40 of the image can be divided into two new cipher patterns without overlapping cells.

  The procedure for generating the cell of the new encryption pattern will be described in detail below.

  As shown in FIG. 5B, for example, “1” of the template 50 (that is, template 51 “1”) is applied to the share pattern 32a according to the conventional visual decryption secret sharing method, and “ When the cell corresponding to “1” is operated so as to be successful, a cell pattern such as the new cipher pattern a42a is obtained. Similarly, a new encryption pattern b42b is obtained by applying the template 52 “2” to the share pattern b32b, and a new encryption pattern b43b is obtained by applying the template 52 “2” to the share pattern b33b.

  As described above, by applying “1” and “2” of the template 50 to each pixel of the shared image A and the shared image B in the conventional visual decoding secret sharing method, the first and second of the present invention are applied. Two types of encryption patterns corresponding to the encryption patterns can be generated.

  The new restoration pattern 42 and the new restoration pattern 43 that are pixels constituting the restored image appear by superimposing the new cipher pattern a and the new cipher pattern b (combination of a series and b series).

  That is, as shown in FIG. 5B, a new restoration pattern 42 appears by superimposing the new cipher pattern a42a and the new cipher pattern b42b, and similarly, a new restoration pattern is created by superimposing the new cipher pattern a42a and the new cipher pattern b43b. A pattern 43 appears.

  Thus, the new restoration pattern 42 and the new restoration pattern 43 form the character portion 46 and the background portion 47 in FIG. 4B, respectively, and the visual effect of the “coarse” pattern and the “dense” pattern. The restoration information can be read by the difference.

  In FIG. 5B, for the sake of understanding, the new cipher pattern a (a series pattern) and the new cipher pattern b (b series pattern) are distinguished by two types of hatching.

    In the encryption recording medium of the present invention, the a-series pattern and the b-series pattern are formed of reflective diffraction gratings having different grating angles. That is, as shown in FIG. 6, the diffraction grating a67 is arranged in the a series pattern in FIG. 3B, and the diffraction grating b68 is arranged in the b series pattern. Thereby, a restored image appears only when a light source having a specific illumination angle is simultaneously illuminated, and the restored image can be made invisible (unreadable) under normal observation conditions. Further, it is possible to superimpose and form two share images (encryption patterns) on a single substrate.

Further, the blank cell 64 shown in FIG. 6 has a configuration in which diffraction gratings having various grating angles and grating pitches are randomly arranged without having a specific angle or pitch.
<Observation state of the encryption recording medium of the present invention>
FIG. 6 is a diagram showing an observation state. FIG. 6 (a) shows a state where image information, which is a normal observation condition, is concealed. FIG. 6 (b) shows an encrypted image by irradiation with a predetermined light source. This represents a state where the decoded information appears after decoding.

  The information cell 61 shown in the figure is a cell to which black is assigned in the description of FIG. 3B, and the information cell 61 is provided with diffraction gratings a62 or diffraction gratings b63 having different grating angles. Yes. In the description with reference to FIG. 6, the diffraction grating arranged in the blank cell 64 is an example in which the grating angles are various angles.

  The appearance of the encryption recording medium 1 of the present invention will be described with reference to FIGS. 6 (a) and 6 (b). In the normal observation state of FIG. 6 (a), the diffraction grating a67 and the diffraction grating a68 have 61 observation images. Like α and 62 observation images β, light is reflected irregularly individually, and the diffraction grating arranged in the blank cell also reflects light irregularly, so that a specific image appears on the encryption recording medium 1. Absent.

  On the other hand, as shown in FIG. 6 (b), the diffraction grating a67 and the diffraction grating a68 simultaneously emit strong light under two light sources having predetermined irradiation angles with respect to the diffraction grating a67 and the diffraction grating b68. Since it is visually recognized with intensity, patterns of “rough” and “dense” appear as in the observation image Σ60, and the character portion 46 and the background portion 47 can be discriminated. That is, the character string “ABC” can be read. In particular, in the background portion of FIG. 6B, the diffraction grating a67 and the diffraction grating a68 are discretely distributed, and irregular reflection of the blank cell 64 is added to this, so that the character portion and the background portion are separated. The difference will stand out even more.

  Note that the diffraction grating has an angle dependency on the angle of the incident light and the line-of-sight angle due to the effect of diffraction and interference on the incident light. That is, the visual light intensity varies depending on the light source position and the viewpoint position. The predetermined light source means a light source having an irradiation angle at which the light intensity from the cell is visually recognized with the highest intensity.

  For example, in FIG. 6B, when a white light source is used as the light source a65 and the light source a66, and the angle formed by the light source a65 and the diffraction grating a67 and the angle formed by the light source b66 and the diffraction grating b68 are arranged in an orthogonal relationship, The new cipher pattern a and the new cipher pattern b are simultaneously recognized with high light intensity, and the character portion 46 and the background portion 47 can be clearly distinguished.

  Further, when the grating angle of the diffraction grating a67 is the angle a and the grating angle of the diffraction grating b68 is the angle b, the larger the difference between the angle a and the angle b, the clearer the restored image. And the angle b are preferably orthogonal.

Even if the diffraction gratings arranged in the blank cell 64 have various grating pitches, irregular reflection occurs in the blank cell 64 under the two light sources having the predetermined irradiation angles. Thus, the same operation as that described in FIG. 6 can be obtained.
<Diffraction grating of information cell and blank cell>
FIG. 7 is a diagram showing the form of the diffraction gratings arranged in the information cell and the blank cell, and the diffraction grating pattern 70 represents the form of the diffraction gratings arranged in the information cell 61 and the blank cell 64. The magnified image A71 and the magnified image B72 are partially magnified images of the diffraction grating pattern 70. The magnified image A71 is an example in which a diffraction grating having an indefinite angle is disposed in the blank cell 64, and the magnified image B72 represents an aspect in which a diffraction grating having an undefined grating pitch is disposed in the blank cell.

  As shown in FIG. 7, the diffraction grating a67 has a specific grating angle a, whereas the blank cell 64 of the enlarged image A71 has various grating angles, and the grating pitch of the enlarged image B72 is There are various pitches (lattice intervals).

  Further, when the diffraction grating of the blank cell 64 is arranged so that the grating angle is different from that of the adjacent cell, the information cell and the blank cell do not continue to have cells having the same grating angle. Since the cells having the same lattice angle do not continue to each other, the distinction between the character portion 46 and the background portion 47 becomes clearer. Further, even when the grating pitch of the diffraction grating of the blank cell 64 is different from that of the adjacent cell, the same effect as in the case of different grating angles can be obtained.

  FIG. 8 is a diagram showing details of the restored image by the encryption pattern of the encryption recording medium of the present invention.

  The restored image 80 indicates that both the first cipher pattern 81 and the second cipher pattern 82 are visually recognized. As a result, the character portion 46 and the background portion 47 can be identified, and “s "Can be read. On the other hand, in a state where either the first cipher pattern 81 or the second cipher pattern 82 can be seen alone, each irregular pattern appears and the character portion 46 and the background portion 47 cannot be distinguished.

  The enlarged boundary image 76 is an enlarged view of the boundary portion between the character portion 46 and the background portion 47. As a result, the cell distribution between the background portion and the character portion is “rough” and “dense”. You can see the difference.

  In FIG. 8, the first cipher pattern 81 and the second cipher pattern 82 are expressed separately for the sake of explanation, but in actuality, they are formed so as to overlap on the same base material.

  The enlarged image 85 is an enlarged view of the cell pattern of the encryption pattern.

  As described above, in order to obtain the restored image 80 from the first cipher pattern 81 and the second cipher pattern 82 formed on the same substrate, both patterns have different lattice angles in the cipher recording medium of the present invention. Formed by a cell.

  As described above, according to the encryption recording medium of the present invention, since two encryption patterns can be formed on the same base material, when obtaining a restored image, an operation for overlaying secret images as in the prior art is performed. Do not need. Further, the transparent medium is not required, and the medium is reduced, so that the cost of the medium can be reduced and the surface does not need to be smooth because it does not need to be in close contact. Since there is no need for a sheet, there are no restrictions on the material and size of the base material.

  In order to produce the encryption recording medium of the present invention, the first encryption pattern and the second encryption pattern may be formed on the substrate by a reflective diffraction grating. In order to form such a diffraction grating, as a well-known method, for example, about 3 μm of a transparent ultraviolet curable resin composition is applied to the surface of a resin substrate, and a mold surface of a diffraction grating replication mold is formed. A diffraction grating is formed by irradiating ultraviolet rays while being in contact with each other to cure the transparent ultraviolet curable resin composition, and then a metal such as aluminum is vacuum-deposited on the surface on which the diffraction grating is formed to increase the thickness. There is a reflective layer of about 100 nm.

  As the base material, various materials such as paper and resin can be used. For example, for card applications, polyvinyl chloride resin, amorphous polyethylene terephthalate (PET-G) resin, polycarbonate resin, polylactic acid resin. and so on. Further, the substrate may be transparent or opaque.

1 Encryption recording medium 10 Original image 11 Share image a
12 share image b
13 Restored image 21 Transparent medium a
22 Medium b
30 pixels of original image 31 division pattern 32 share pattern 33 share pattern 40 pixels of original image 41 new division pattern 42 new restoration pattern 43 new restoration pattern 45 cells 46 character part 47 background part 50 template 61 information cell 67 diffraction grating a
68 Diffraction grating b
80 restored image 81 first encryption pattern 82 second encryption pattern

Claims (5)

A first cipher pattern and a second cipher pattern, which are generated from a cipher image by the visual decryption secret sharing method, are formed by superimposing on the base material,
The first cipher pattern and the second cipher pattern are composed of a set of information cells and blank cells arranged in a small area obtained by dividing each pixel constituting the cipher image,
In the encryption recording medium arranged such that the first information cell constituting the pixel of the first encryption pattern and the second information cell constituting the pixel of the second encryption pattern do not overlap each other,
The first information cell and the second information cell are formed by diffraction gratings having different grating angles,
The blank cell is formed by a diffraction grating having a lattice angle of an indefinite angle for each cell.   2. The encryption recording medium according to claim 1, wherein the blank cell is formed by a diffraction grating having a grating angle different from that of an adjacent cell. A first cipher pattern and a second cipher pattern, which are generated from a cipher image by the visual decryption secret sharing method, are formed by superimposing on the base material,
The first cipher pattern and the second cipher pattern are composed of a set of information cells and blank cells arranged in a small area obtained by dividing each pixel constituting the cipher image,
In the encryption recording medium arranged such that the first information cell constituting the pixel of the first encryption pattern and the second information cell constituting the pixel of the second encryption pattern do not overlap each other,
The first information cell and the second information cell are formed by diffraction gratings having different grating angles,
The blank cell is formed by a diffraction grating having a grating pitch indefinite for each cell.   4. The encryption recording medium according to claim 3, wherein the blank cell is formed by a diffraction grating having a grating pitch different from that of an adjacent cell. 5. The encryption recording according to claim 1, wherein the grating angle of the diffraction grating forming the first information cell and the grating angle of the diffraction grating forming the second information cell are orthogonal to each other. Medium.

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