JP2011027942A - Cryptogram recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cryptogram recording medium, wherein two cryptogram images are overlapped with each other to restore an original pattern by using a visual decoding type encryption technology, for allowing easy visual recognition of a restored image in restoration to easily discriminate a hidden pattern. <P>SOLUTION: With a conventional technology, the shape of a hidden pattern is determined from the background of an irregular pattern in discrimination of a restored image. In this cryptogram recording medium, the original pattern is represented by a segment display system, so that the hidden pattern can be discriminated based on whether each of segments is bright or dark, and consequently discrimination of the pattern is facilitated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an encryption recording medium in which shape information concealed in a state in which a recorded image cannot be visually recognized in a normal state is visualized by superimposing a decryption filter.

  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. However, these examples are for one-time use (disposable), and when they are not used, they maintain a high level of confidentiality. Have difficulty.

There is a visual decryption type encryption technique as one of the techniques for the above demand. 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 discloses a technique relating to the configuration and production of a recording medium that uses visual decryption encryption technology to conceal information without using a concealment layer or the like.
Various methods have been proposed for visual decryption encryption technology, share 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.

  As described above, the visual decryption encryption technology is advantageous in that it can be restored by visual manual operation. On the other hand, since the original image is restored by overlapping a plurality of share images, There is a weakness that the original image must be deciphered from irregular patterns (called share patterns). FIG. 1 is a diagram showing a process of encryption and restoration using visual decryption encryption technology. For example, the shape of “T” in the restored image 13 in FIG. 1 is likely to be buried in a background share pattern. In addition, even if there is a slight shift in the overlap, a white portion appears and the contrast with the background becomes small, so that there is a problem that it becomes more difficult to distinguish the image to be restored from the background.

  That is, in the restoration technique exemplified in the above document, the original image is discriminated from the irregular pattern of the share image (referred to as a share pattern), but in the coarse share pattern, as shown in FIG. The image is difficult to discriminate, and as the share pattern becomes finer as shown in FIG. 2B, the restored image becomes easier to discriminate. However, on the other hand, more precise positioning accuracy is required.

JP 2001-118122 A

M.Naor andA.Shamir, "Visual Cryptography", Proc. Of Eurocrypt'94 May 1994

  Therefore, the present invention provides an encryption recording medium in which a restored image can be easily visually recognized and a hidden symbol can be easily distinguished when restoring an original image from two shared images while using a visual decryption type encryption technique. It is an issue to provide.

The present invention for solving the above problems
A set of the first recording medium and the second recording medium having visible transparency,
Of the first and second encrypted images generated from the original image by the visual decryption secret sharing method, the first encrypted image is at a predetermined position of the first recording medium, and the second encrypted image is An encryption recording medium formed at a predetermined position of the second recording medium, wherein the second encryption image is superimposed on the first encryption image and the original image is recognizable so as to be visible;
The original image is a pattern formed by a segment display pattern.
Further, the encrypted image is formed of a segment display pattern.

  According to the encryption recording medium of the present invention, the restored image is expressed by the brightness of each segment in the segment format, so that the hidden symbols can be easily read.

Conceptual diagram of visual decryption encryption technology The figure which shows the restoration picture of visual decryption type encryption technology (difference of density) The figure which shows the encryption recording medium of this invention Figure showing a shared image The figure which shows the production | generation process of the share image of the encryption recording medium of this invention The figure which shows the other aspect of the encryption recording medium of this invention

Hereinafter, the details of the present invention will be described with reference to FIGS.
Hereinafter, the first recording medium is referred to as medium A, the second recording medium as medium B, the first encrypted image as shared image A, and the second encrypted image as shared image B.

FIG. 3 shows a configuration example of the encryption recording medium of the present invention.
As shown in FIG. 3A, the encryption recording medium of the present invention includes a medium A31 and a medium B33, and the share image A32 is the first medium A31 and the share image B34 is the visible medium B33. Each is formed.
FIG. 3A shows a state in which the medium B33 is to be overlaid on the medium A31. For convenience of overlay alignment, other than the share patterns on the medium A31 and the medium B33. It is desirable to provide a register mark or the like in the area (not shown).
FIG. 3B is an enlarged view of the share image A32 and the share image B34, and shows that the share images A and B are configured in a segment display form.

  As shown in FIG. 3C, the segment display format is an expression method for expressing a symbol by a combination of segments 35. Symbols, numbers, symbols, and other shapes can be expressed as symbols. As a typical segment display pattern, a 7-segment type 36 and a 14-segment type 37 as shown in the figure are known. For example, when a four-digit number “4720” is represented in a 7-segment display format, an aspect like the segment display example 38 is obtained.

FIG. 4 shows each share image and its restored image of the encryption recording medium of the present invention.
When the shared image 32 and the shared image 34 are overlapped at a predetermined position, the shades of the segments (“bright” and “dark”) appear as shown in the restored image 40, and the shape of the pattern of the original image can be read. Become.

  In the conventional method, as shown in FIG. 1, the restored image 13 interprets the shape of the symbol from the share pattern that is the background of the symbol. However, according to the segment display format as in the present invention, the symbol is interpreted. Is extremely easy. That is, in the example of the restored image 13 in FIG. 1, the ratio of “black” and “white” of the share pattern that is the background of the character is 50:50. However, in the case of the encryption recording medium of the present invention, it is possible to discriminate between “bright” and “dark” of the segment, so that it is very easy to read the design.

FIG. 5 is a diagram illustrating a process for producing a shared image.
(A) represents an aspect of the original image, and here, a 4-digit number “4720” is represented in a 7-segment format.
(B) represents two shared images generated from the original image by the visual decryption secret sharing method.
(C) represents a mask having a 7-segment pattern, and the share image of (b) is cut out with a 7-segment pattern (mask processing).
(D) is the share image (share image A and B) represented by the shape of the segment display format.
The above is the generation process of the share images A and B. (e) represents a state in which the share image A and the share image B are overlapped.

The encryption recording medium of the present invention is not limited to the above embodiments, and the embodiment shown in FIG. 6 is also included in the present invention.
FIG. 6A shows the encryption recording medium shown in FIGS. 3 to 5, and the figure shows that a shared image having a segment format shape is generated from an original image having a segment format shape. As a result, the restored image also has a segment form.
FIG. 6B shows a mode in which the share image generated from the original image is generated without being processed into the segment format shape, and the restored image obtained from this has a background of the share pattern unlike (a).
FIG. 6C shows one of two share images cut out in a segment format, and the restored image has a share pattern background as in FIG.
The symbols to be restored in FIGS. 6 (b) and 6 (c) are represented in the segment format, and the interpretation is easy as in the case of (b).

In order to produce the encryption recording medium of the present invention, the share images A and B may be formed on a sheet-like substrate by printing or the like. There are various base materials for the share medium A, such as paper and resin sheets. For example, for card applications, polyvinyl chloride resin, amorphous polyethylene terephthalate (PET-G) resin, polycarbonate resin, polylactic acid resin. and so on. Further, the base material for the share medium A may be transparent or opaque.
Further, a transparent polymer is suitable as the base material for the share medium B, and examples thereof include polyvinyl chloride resin, amorphous polyethylene terephthalate (PET-G) resin, polycarbonate resin, and polylactic acid resin. .

10 Original image 11 Share image a
12 share image b
13 Restored image 21 Coarse share pattern 22 Fine share pattern 31 Medium A
32 share image A
33 Medium B
34 Share image B
40 Restored image 41 “Bright” segment 42 “Dark” segment

Claims (2)

A set of the first recording medium and the second recording medium having visible transparency,
Of the first and second encrypted images generated from the original image by the visual decryption secret sharing method, the first encrypted image is at a predetermined position of the first recording medium, and the second encrypted image is An encryption recording medium formed at a predetermined position of the second recording medium, wherein the second encryption image is superimposed on the first encryption image and the original image is recognizable so as to be visible;
The encryption recording medium, wherein the original image is a pattern formed by a segment display pattern 2. The encryption recording medium according to claim 1, wherein the encryption image is configured by a segment display system pattern.

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