JP2012063544A - Cipher recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cipher recording medium capable of easily discriminating printing elements and a background portion of a reproduced image when restoring an original image from two share images despite using a visual secret sharing scheme.SOLUTION: In two cipher images generated by the visual secret sharing scheme, a cipher image by a diffraction grating 22 is formed on a substrate 21, and a cipher image by a concealing layer is formed on a transparent substrate 25. Cipher patterns are colored with different colors respectively. When a medium B6 is superposed on a medium A5 at a prescribed position, the background portion of the restored image is concealed by the concealing layer 26 such that irregular patterns of the concealing layer 26 are observed, while, in the printing elements, patterns by the diffraction grating 22 appear such that the background portion and the printing elements are clearly discriminated by the visual effect unique to the diffraction grating so as to decipher the shape of the printing elements.

Description

  The present invention relates to an encryption recording medium that is recorded in an irregular pattern encrypted so that the recorded image cannot be visually recognized in a normal state, and is visualized by superimposing a decryption pattern at the time of restoration. .

  A technique for confirming the authenticity of a product or article using a hologram made of a diffraction grating has been widely used. A typical usage is to process a hologram into a seal shape and attach it to an article as an authenticity determination medium. The reason why holograms are heavily used in the field of anti-counterfeiting is the convenience of “seeing” due to its unique visual effect and the difficulty of forgery due to the need for microfabrication technology for production. However, in recent years, as a manufacturing technique of a diffraction grating is known, forgery of holograms has come to the market, and a higher level of forgery prevention effect is desired for holograms.

  On the other hand, there is a visual decryption type encryption technique as a technique excellent in information concealment while having the simplicity of “understandable”. This is to process the original image information into an image that cannot be visually recognized by dispersing it into a plurality of encrypted images (called shared images) composed of irregular patterns, and superimposing these shared images. Thus, the original image information is restored (that is, decoded) to a visible state. In this way, in order to restore the original information from multiple shared images, a plurality of media on which the shared images are recorded are also used, but no special equipment is required for restoration, and it is easy to understand just by looking at the results Is a feature.

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 described above, the visual decryption type encryption technology has an advantage of simplicity that can be restored by visual manual operation. However, since the original image is restored by superimposing a plurality of shared images, a plurality of media are restored. It is necessary to superimpose them precisely.

FIG. 6 is a diagram showing the process of encryption and restoration using the visual decryption secret sharing method. As shown in FIG. 6, in the encryption process, the original image 10 is a share of irregular patterns. It is decomposed into images. In the share image A11 and the share image B12 generated in this way, an irregular pattern is only visually recognized independently, and significant information cannot be read.

Thus, in the normal visual decoding secret sharing method, each pixel constituting the shared image is constituted by a set of white and black cells. Here, assuming that a shared image is created by printing or the like, a white cell refers to an area where nothing is applied, and a transparent object such as a film is an area that remains transparent. A black cell refers to a region to which a color material such as ink is applied, and is shown in black in FIG. 6, but the color material applied to the black cell is not limited to black and is a chromatic color. May be.

In order to restore the original image from the share image, the share image A11 and the share image B12 may be superimposed at a predetermined position. As a result, a pattern such as the restored image 13 appears, and as shown in FIG. 6, the shape of “T” of the original image (referred to as “image line portion” with respect to the background portion) is obtained with the irregular pattern as the background portion. Can be read. This is because the background portion has an irregular pattern in which black and white are mixed, whereas the image line portion is filled with black, and therefore the image line portion appears due to the difference in shading.
Thus, only the black cells form the image line portion representing the shape of the original image, and the white cells are distributed only in the background portion. Therefore, in the present invention, the cells corresponding to the black cells are formed. Is called an information cell 15 and a cell corresponding to a white cell is called a blank cell 16.

  By the way, in the shared image made up of white and black cells as shown in FIG. 6, a white portion appears even if there is a slight misalignment at the time of restoration. There is a problem that it is difficult to distinguish an image from a background. FIGS. 7A and 7B show the form of the restored image based on the presence or absence of misalignment. In the restored image 73 without misalignment, the shape of “8” can be read, but the superimposed image is positioned. In the restored image 74 having a deviation, the visibility is remarkably deteriorated, and it becomes difficult to discriminate between the image line portion and the background portion.

  Accordingly, an object of the present invention is to provide an encryption recording medium in which a restored image can be easily read when restoring an image that is a superposition source of two shared images while using a visual decryption type secret sharing method. To do.

The encryption recording medium of the present invention that solves the above problems is as follows.
The recording medium in which the first encrypted image is formed on the first substrate and the recording medium in which the second encrypted image is formed on the second substrate having visible transparency are used as a set. The encrypted image is generated from the original image by the visual decryption secret sharing method, the first encrypted image is at a predetermined position on the first base material, and the second encrypted image is on the second base material. Each of the original images can be visually recognized when viewed from the surface side of the second base material by overlapping the second encrypted image on the first encrypted image. An encryption recording medium for decrypting
The first encrypted image and the second encrypted image are composed of a set of cells in which each pixel constituting the encrypted image is divided in a matrix, and the cell is composed of either an information cell or a blank cell. The information cells in the first encrypted image are formed by a diffraction grating on the first substrate, and the information cells in the second encrypted image are formed by a concealing layer on the second substrate. It is formed.

    According to the encryption recording medium of the present invention, when the two media are overlapped, the background part is concealed with the diffraction grating pattern, while the image line part is formed with the diffraction grating pattern. The image area can be clearly seen by the visual effect. Therefore, the restored image can be visually recognized without the need for strict alignment with respect to the positional accuracy at the time of superposition. In particular, there is an effect that labor of trial and error required for manual alignment is remarkably reduced.

The figure which shows the encryption recording medium of this invention The figure which shows the structure of the encryption recording medium of this invention A diagram showing an encryption pattern by a conventional visual decryption secret sharing method The figure which shows the encryption pattern of the encryption recording medium of this invention The figure which shows the mode of the decompression | restoration by the encryption recording medium of this invention Conceptual diagram of visual decryption secret sharing method The figure which shows the restoration picture by the conventional visual decoding type secret sharing method The figure which shows the structural example of the encryption recording medium of this invention

FIG. 1 is a schematic diagram of a forgery determination medium of the present invention.
The encryption recording medium 1 of the present invention includes a medium A5 and a medium B6. FIG. 1 shows a medium A5 on which an encryption image a7 corresponding to the first encryption image is recorded and an encryption image b8 corresponding to the second encryption image. This represents a state in which the recorded medium B6 is overlaid. The base material of the medium B6 has visible transparency, and the restored image 9 appears when the encrypted image a7 and the encrypted image b8 are overlapped at a predetermined position. The encrypted image a7 and the encrypted image b8 are share images generated by the visual decryption secret sharing method.

FIG. 2 is a configuration diagram of a forgery determination medium according to the present invention, showing a state in which a medium B6 is superimposed on a medium A5 at a predetermined position, and cells of both media are overlapped.
The medium A5 has an information cell formed by the first base material (base material 21) and the diffraction grating 22, while the medium B6 is formed by the second base material (transparent base material 25) and the concealing layer 26. It has an information cell formed. Note that cells other than information cells are blank cells.
When the encryption recording medium 1 is observed from the direction of the line of sight in the state of being overlapped in this way, the portion of the information cell of the medium A5 where the information cell of the medium B6 overlaps is concealed by the concealment layer 26. The grid becomes invisible. In addition, a place where there is no concealing layer 26 (blank cell) is in a transparent state through the transparent base material 25, and if there is a diffraction grating 22 in the same place of the medium A5, reflected light from the diffraction grating 22 is visible.

Hereinafter, the features of the present invention will be described in detail with reference to FIGS.
First, a share pattern based on the conventional visual decryption secret sharing method will be described.
As shown in FIG. 3, the share pattern by the conventional visual decryption encryption technology is a cell that is a small region of an integer ratio (2 × 2 in the example) of pixels constituting the original image (pixel 30 of the original image). Is generated by assigning white (margin cell) or black (information cell) to each cell 35 formed by the division. A set of cells in which white or black is arranged in this way is called a share pattern.

  The share pattern generated in this way is a pixel constituting the share image A and the share image B. That is, the pattern of the share pattern a (reference numeral 32a) and the share pattern a (reference numeral 33a) is a pixel of the share image A, and the pattern of the share pattern b (reference numeral 32b) and the share pattern b (reference numeral 33b) is a pixel of the share image B. It becomes. When restoring the original image by superimposing the share image A and the share image B, the superposition of two patterns such as the share pattern a (32a) and the share pattern b (32b) is like the restored pixel 32. The pixel representing the “background portion” where “white” and “black” are crossed, and the overlapping of the two patterns of the share pattern a (33a) and the share pattern b (33b) is only “black” like the restored pixel 33 This represents a pixel representing the “image portion”.

Next, the encryption pattern of the encryption recording medium of the present invention will be described.
In generating the encryption pattern of the encryption recording medium of the present invention, as shown in FIG. 4, first, it is divided into cells 45 which are 2 × 2 small areas as in FIG. Here, in the encryption pattern of the present invention, a diffraction grating or a concealing layer is arranged in the information cell 46 of the cells 45 in place of the black. That is, when a diffraction grating is arranged in the share pattern a series and a concealment layer is arranged in the share pattern b series, the share patterns 42a and 43a composed of information cells of the diffraction grating and the information cells of the concealment layer are used. 42b and 43b share patterns are generated. As a result, the pattern of the share pattern a (symbol 42a) and the share pattern a (symbol 43a) becomes a pixel constituting the share image A, and the pattern of the share pattern b (symbol 42b) and the share pattern b (symbol 43b) is the share image. This is a pixel constituting B.
In FIG. 4, the diffraction grating and the concealing layer are differently shaded for distinction.

  When the share image A and the share image B are overlapped, the overlap of the two patterns such as the share pattern a (42a) and the share pattern b (42b) becomes a pixel representing the “background portion” like the restoration pixel 42. The overlap of the two patterns of the share pattern a (43a) and the share pattern b (43b) becomes a pixel representing the “image portion” like the restored pixel 43.

  As a result, in the portion where the diffraction grating and the concealing layer overlap, the diffraction grating is concealed by the concealing layer, so that only the concealing layer appears as shown in the restoration pixel 42. The restored pixel 42 forms a background portion. In addition, the image area representing the shape of the original image appears as a region filled with the diffraction grating and the concealing layer. Thus, since the visual effect is different between the background portion where the diffraction grating is not visible and the image line portion where the diffraction grating is scattered and viewed, the shape of the image line portion can be clearly read.

FIG. 5 is a diagram showing a process of encryption and restoration in the encryption recording medium of the present invention.
First, the original image 10 is decomposed into a share image A11 and a share image B12 using a visual decryption type secret sharing method. Subsequently, in the encryption recording medium of the present invention, a diffraction grating having a predetermined grating angle, grating pitch, and grating density is arranged in the “black” region of the share image A11 (grating image 51). Further, a concealing layer having a characteristic of shielding visible light is arranged in the “black” region of the share image B12 (concealing layer image 52).
In FIG. 5, the diffraction grating 55 is represented by black solid and the concealing layer 56 is represented by shading to distinguish the two.

When a grating image 51 composed of a diffraction grating 55 and a concealing layer image 52 composed of a concealing layer 56 are superimposed at a predetermined position with the concealing layer image 52 facing upward, a restored image 53 appears. At this time, since the diffraction grating 55 is concealed by the concealing layer 56 in the “background part”, the diffraction grating cannot be seen and an irregular pattern of the concealing layer 56 appears. On the other hand, the “image portion” appears in a state where the diffraction grating cells 58 and the concealing layer cells 59 are irregularly distributed. As a result, in the “image area”, the appearance of the background area and the image area is different due to the visual effects peculiar to the diffraction grating, such as the angle dependency of reflected light and the appearance of interference colors. The “T” shape of the original image can be visually recognized.
Further, even if there is a slight shift as seen in FIGS. 8C and 8D in the superimposed shared images, there is a difference in color and gloss between the background portion and the image line portion. The shape of the part is clearly visible.

FIG. 8 shows a configuration example of the encryption recording medium of the present invention, and FIG. 8A of a configuration example equivalent to FIG. 2 is also shown for comparison.
In FIG. 8B, the medium A5 and the medium B6 are overlapped so that the concealing layer 25 and the diffraction grating 22 are in close contact with each other, and the concealing layer 26 is observed through the transparent substrate 25. The configuration of FIG. 8B has an advantage that no parallax occurs when observing because the shielding layer 25 and the diffraction grating 22 are in close contact with each other.
In the configuration of FIG. 6B, since the surface on which the concealing layer 26 is formed and the surface on which the diffraction grating 22 is formed are overlapped with each other, the diffraction grating 22 and the concealing layer 26 are attached to the base material. When viewed from the same plane, they are mirror images of each other.

As the base material of the encryption recording medium of the present invention, various materials can be applied. Examples of the base material suitable for the medium A5 include paper and resin sheets. For example, for card use, a polyvinyl chloride resin, Examples include amorphous polyethylene terephthalate (PET-G) resin, polycarbonate resin, and polylactic acid resin. Further, the base material for the medium A5 may be transparent or opaque.
As the base material for the medium B6, a polymer having transparency is suitable, and examples thereof include polyvinyl chloride resin, amorphous polyethylene terephthalate (PET-G) resin, polycarbonate resin, and polylactic acid resin.

As a simple method, the masking layer 26 can be formed on a sheet-like substrate by using a light-shielding ink by printing or ink jetting. As the ink to be used, no special ink is required, and an easily available pigment-type color material ink can be applied. Further, the color of the masking layer 26 is not limited to black, and may be white or chromatic.
The diffraction grating 22 is preferably a reflective type having good visibility, and can be created by adding a reflective film such as aluminum vapor deposition to the diffraction grating formed on the surface of the resin sheet. In addition, the diffraction grating can change the visual effect such as the angle, intensity, and color of reflected light by changing the grating angle, grating pitch, grating density, etc. It is also possible to add decorativeness to the recording medium.

1 Cryptographic recording medium 5 Medium A
6 Medium B
7 Encrypted image a
8 Encrypted image b
9 Restored image 10 Original image 11 Share image A
12 share image B
DESCRIPTION OF SYMBOLS 21 Base material 22 Diffraction grating 25 Transparent base material 26 Concealment layer 30 Original image pixel 31 Division pattern 40 Original image pixel 41 Division pattern 42 Restoration pixel 43 Restoration pixel 51 Grid image 52 Concealment layer image 53 Restoration image

Claims (1)

A recording medium in which the first encrypted image is formed on the first substrate and a recording medium in which the second encrypted image is formed on the second substrate having visible transparency
The first and second encrypted images are generated from the original image by a visual decryption secret sharing method, the first encrypted image is at a predetermined position on the first base material, and the second encrypted image is the first encrypted image. Each of the two base materials is formed at a predetermined position and the second cipher image is superimposed on the first cipher image and viewed from the surface side of the second base material. An encryption recording medium for decrypting the image to be visible,
The first encrypted image and the second encrypted image are composed of a set of cells in which each pixel constituting the encrypted image is divided in a matrix, and the cells are composed of either information cells or blank cells. The information cells in the first encrypted image are formed by a diffraction grating on the first substrate, and the information cells in the second encrypted image are formed by a concealing layer on the second substrate. An encryption recording medium on which invisible information is superimposed, characterized by being formed.

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