JP2004364093A - Secret information processing system, device and method for embedding secret information, and device and method for detecting secret information - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secret information processing system capable of processing secret information without needing a special seal, etc., and without having to manage a cryptographic key (for example, password) for releasing the secret information. <P>SOLUTION: A secret information embedding device 10 encrypts the secret information with inherent information inherent to an acknowledger given authority that approves the release of the secret information as a cryptographic key. A secret information detecting device 30 decrypts the secret information with the inherent information as a decryption key to display the secret information only when the inherent information (for example, an approved mark, sign, etc.,) inherent to the acknowledger is given to a printed document 20 being a paper medium. Since a physically approving method such as the approved mark and the signature on the paper medium is used to decrypt digital cryptograph in this way, the special seal, etc., is not needed and the cryptographic key (for example, password) for releasing the secret information does not have to be managed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a secret information processing system for exchanging secret information (also referred to as confidential information, confidential information, and the like) that is desired to be kept secret from a third party by using a sheet of paper as a medium, and related technology.
[0002]
[Prior art]
In recent years, various methods of exchanging confidential information, such as mobile phone billing and qualification test numbers, which are not desired to be seen by a third party using paper as a medium have been attempted. As an example of such secret information processing, when sending secret information, a special seal that loses adhesiveness once it is peeled off is used to send the information as a postcard instead of a sealed letter. For example, a special sticker is attached to a place where confidential information is described, or the entire postcard is specially sealed by folding a sheet twice as large as a postcard (for example, see Patent Document 1). ). If a third party removes the special seal to view confidential information, or opens the specially sealed postcard in two, it cannot be recovered again. Since a trace that the confidential information was seen by a third party remains, it is possible to suppress the third party from seeing the confidential information.
[0003]
As another method of secret information processing, a method is known in which secret information is encoded with a two-dimensional barcode or the like and printed on paper (for example, see Patent Document 2). In this technique, generally, secret information is encrypted, then bar-coded, and printed on paper. Then, when taking out the secret information from the paper, the data can be read from the barcode portion, and then a separately prepared encryption key (for example, a password) can be input to obtain the secret information.
[0004]
[Patent Document 1]
JP-A-8-156458
[Patent Document 2]
JP-A-2000-62357
[0005]
[Problems to be solved by the invention]
However, the above-described conventional secret information processing method has the following problems. First, in the case of a method using a special seal, a special seal, a technique for attaching the seal, or a technique for creating a special postcard are required, which is costly and troublesome. Further, in the case of encoding secret information using a two-dimensional barcode or the like, it is necessary to manage an encryption key (for example, a password) for each document, which is troublesome. Further, if the confidential information can be made public by an authorized person, it is necessary to widely inform an encryption key (for example, a password) for reading the encrypted confidential information.
[0006]
The present invention has been made in view of the above problems of the conventional secret information processing method, and an object of the present invention is to eliminate the need for a special seal or the like and to provide an encryption key for disclosing secret information. Provided is a new and improved secret information processing system, a secret information embedding device, a secret information detection device, a secret information embedding method, and a secret information detection method capable of processing secret information without having to manage (for example, a password). That is.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, according to a first aspect of the present invention, a secret information embedding device that embeds secret information in a document by using a digital watermark, and detects secret information embedded in the document by using a digital watermark. A confidential information processing system (1) for exchanging confidential information with a confidential information detecting device by using a document as a medium is provided, the system including the following components (claim 1).
[0008]
The secret information embedding device includes a document image forming unit (11) for creating a document image (for example, for each page) based on the document data, and an approver who is authorized to approve the release of the secret information. A unique information database (17) for managing unique information of a document, a watermark image forming unit (12) for encrypting secret information using the unique information as an encryption key and forming a watermark image based on the secret information, a document image and a watermark image And an output unit (14) for outputting a watermarked document based on the above.
[0009]
The secret information detection device includes an input unit (31) for receiving a watermarked document and generating a watermarked document image (a document image and a watermark image superimposed), and secret information encrypted from the watermarked document image. A secret information detecting unit (32) for detecting the secret information, and when the watermarked document has been given unique information unique to an approver who has been authorized to approve the release of the secret information, the unique information is extracted. A unique information extraction unit (34); a decryption processing unit (35) for decrypting the secret information using the unique information as a decryption key; and a secret information display unit (36) for displaying the secret information. (Claims 1 and 13).
[0010]
According to such a system, the secret information is encrypted using the unique information unique to the approver who has been authorized to approve the disclosure of the secret information as the encryption key. Only when the printed document (watermarked document) of the paper medium is given unique information unique to the approver (for example, an approval mark or a signature), the secret information is decrypted using the unique information as a decryption key. , To display confidential information. As described above, since the physical approval method of performing an approval stamp or signature on a paper medium is used for decryption of digital encryption, it is not necessary to manage an encryption key (for example, a password) for disclosing secret information. Furthermore, the fact that the approval mark or signature is given to the paper medium means that the confidential information can be made public. Easy.
[0011]
The following application is possible in the secret information processing system, secret information embedding device, and secret information detecting device of the present invention.
[0012]
First, regarding the secret information embedding device, for example, the following information can be adopted as the unique information unique to the approver embedded by the secret information embedding device.・ Information on the seal imprint of the seal owned by the approver (Claims 2 and 9)
-Information on the signature of the approver (claims 3, 10)
[0013]
Seals and signatures are characterized by being hard to be imitated by others and immutable. Since the seal is generally owned only by the person, the seal can be used to identify the person. Especially in Japan, seals play an important role in identifying individuals. In addition, since a signature can be generally written only by the person himself / herself, it can be used for identification of the person like a seal. Especially in the United States, signatures play an important role in personal identification. In addition, a seal is easy to detect when it is lost or stolen, and the signature has the effect of not having to worry about loss or theft in the first place.
[0014]
In addition, by making the unique information irreversible in which the approver cannot be specified, it is possible to keep secret the approver who has been authorized to approve the disclosure of the secret information ( Claims 4 and 11).
[0015]
If the unique information is given to a predetermined area of the watermarked document, the unique information can be easily detected when the secret information is detected (claims 5 and 12).
[0016]
On the other hand, the secret information detecting device further includes a unique information area extracting unit (33) for extracting an area to which unique information of the watermarked document is given, and the unique information extracting unit (34) includes a unique information area extracting unit (33). ) Can also extract unique information from the region extracted (claims 6 and 14).
[0017]
Further, in this case, the unique information area extraction unit (33) can also extract an area to which the unique information of the watermarked document is given by detecting a changed portion of the watermarked document (claim). Items 7, 15).
[0018]
According to such a configuration, it is possible to easily detect the unique information even when the unique information is provided at an arbitrary position.
[0019]
According to another aspect of the present invention, there is provided a secret information embedding method for embedding secret information in a document using a digital watermark, the method including the following steps. Item 16).
.A document image forming process for creating a document image (for example, for each page) based on the document data
A watermark image forming step of encrypting the secret information using unique information unique to the approver who has been authorized to approve the disclosure of the secret information and forming a watermark image based on the encrypted secret information;
An output step of outputting a watermarked document based on the document image and the watermark image
[0020]
According to another aspect of the present invention, there is provided a secret information detecting method for detecting secret information embedded in a document using a digital watermark, the method including the following steps. (Claim 17).
An input step of receiving a watermarked document and generating a watermarked document image
.A secret information detection step of detecting encrypted secret information from a watermarked document image
• If the watermarked document has been given unique information unique to the approver who has been authorized to approve the release of confidential information, a unique information extraction step for extracting the unique information
.Decryption processing step of decrypting secret information using unique information as a decryption key
・ Confidential information display process for displaying confidential information
[0021]
In addition, the method further includes a unique information area extracting step of extracting an area to which the unique information of the watermarked document is given, and the unique information extracting step includes a step of extracting unique information from the area extracted in the unique information area extracting step. It is also possible (claim 18).
[0022]
According to this method, it is possible to easily detect the unique information even when the unique information is provided at an arbitrary position.
[0023]
Note that, in the above description, the components described in parentheses merely indicate corresponding components and signals in the embodiments described below for easy understanding, and the present invention is not limited thereto.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a secret information processing system, a secret information embedding device, a secret information detecting device, a secret information embedding method, and a secret information detecting method according to the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted.
[0025]
In the present embodiment, an approver who is authorized to approve the disclosure of confidential information for a document in which confidential information is encrypted and printed is stamped as unique information unique to the user (an information disclosure approval seal). ) Will be described as an example of a system that allows anyone to view confidential information.
[0026]
FIG. 1 is a diagram illustrating a configuration of a secret information processing system according to the present embodiment.
As shown in FIG. 1, a secret information processing system 1 includes a secret information embedding device 10 that embeds secret information in a document using a digital watermark, and a secret information that detects secret information embedded in a document using a digital watermark. This is a system for exchanging secret information with the detection device 30 using the print document (paper) 20 as a medium.
First, the secret information embedding device 10 will be described.
[0027]
(Secret information embedding device 10)
The secret information embedding device 10 is a device that expresses secret information on paper in a form that cannot be deciphered by human eyes, and generates a document in which the secret information is embedded. As shown in FIG. 1, the secret information embedding device 10 includes a document image forming unit 11, a watermark image forming unit 12, a watermarked document image synthesizing unit 13, and an output unit 14. The document data 15 is data created by a document creation tool or the like. The secret information 16 is arbitrary information (character strings, images, audio data) to be embedded in a paper medium in a format other than characters.
[0028]
(Document Image Forming Unit 11)
The document image forming unit 11 creates a document image for each page based on the document data 15. The document image is an image in which the document data 15 is printed on paper. Specifically, a white pixel area in the document image is a part where nothing is printed, and a black pixel area is a part where black paint is applied. FIG. 2 is an explanatory diagram illustrating an example of a document image. Note that, in the present embodiment, description is made on the assumption that printing is performed with black ink (single color) on a white paper surface. However, the present invention is not limited to this, and the same applies when printing is performed in color (multicolor). The present invention can be implemented.
[0029]
(Watermark image forming unit 12)
The watermark image forming unit 12 forms a watermark image to be embedded in a document based on the secret information 16 and the imprint characteristic data 17. The secret information 16 is arbitrary information (character strings, images, audio data) to be embedded in a paper medium in a format other than characters. The seal imprint feature data 17 is obtained by extracting a certain invariant feature from the seal imprint of the seal and converting it into data. In the secret information embedding device 10, the imprint characteristic data 17 is managed by being made into a database.
[0030]
The formation of a watermark image by the watermark image forming unit 12 will be described.
First, the watermark image forming unit 12 sets a person (authorizer) who is authorized to approve publication according to the secret information 16 and extracts the seal stamp feature data 17 of the authorizer. Then, the secret information 16 is encrypted using the imprint characteristic data 17 of the approver as an encryption key. Then, the encrypted secret information is digitized and converted into a numerical value, which is then subjected to N-element encoding (N is 2 or more). Then, each code is assigned to N types of signals prepared in advance. The watermark image is an image in which these N types of signals are arranged according to a certain rule.
[0031]
Examples of such digital watermarking techniques include, for example, documents (Japanese Patent Application No. 2001-217758, “Watermark Information Embedding Device and Watermark Information Detecting Device”, and Japanese Patent Application No. 2002-177086, “Watermark Information Embedding Device and Watermark Information Detecting Device”). ). The watermark image embedding device disclosed in this document prepares a plurality of dot patterns in which the direction and / or wavelength of a wave is changed according to the arrangement of dots, gives one symbol to one dot pattern, and By arranging them in combination, confidential information is given to the document. In the present embodiment, the digital watermark technology disclosed in this document can be used. By embedding the secret information in the document as a digital watermark, there is an effect that the existence of the secret information is hardly recognized by a third party.
[0032]
The technique disclosed in the above document is merely an example for realizing the function of the watermark image forming unit 12, and therefore, a more detailed description will be omitted. It goes without saying that other digital watermarking technology may be employed to realize the function of the watermark image forming unit 12.
[0033]
(Watermarked Document Image Synthesis Unit 13)
The watermarked document image synthesizing unit 13 creates a watermarked document image by superimposing the document image formed by the document image forming unit 11 and the watermark image formed by the watermark image forming unit 12. FIG. 3 is an explanatory diagram showing an example of a watermarked document image in which secret information is embedded. The encrypted data and the tampering detection data are represented by a dot pattern and cannot be deciphered by human eyes.
[0034]
(Output unit 14)
The output unit 14 is an output device such as a printer, and prints the watermarked document image created by the watermarked document image combining unit 13 on a paper medium. When the output unit 14 is a printer, the above-described document image forming unit 11, watermark image forming unit 12, and watermarked document image synthesizing unit 13 may be realized as one function of a printer driver.
[0035]
The secret information embedding device 10 has been described above.
The print document 20 is printed by embedding the secret information 16 in the original document data 15 and is a document that is physically stored and managed, such as being distributed or circulated.
Next, the secret information detection device 30 will be described.
[0036]
(Secret information detection device 30)
The confidential information detection device 30 extracts the confidential information from the printed document 20 in which the confidential information is embedded when the seal of the approver who has been authorized to approve the disclosure of the confidential information is pressed. It is a device for displaying. As shown in FIG. 1, the secret information detection device 30 includes an input unit 31, a secret information detection unit 32, a seal stamp area extraction unit 33, a seal imprint feature extraction unit 34, a decryption processing unit 35, and a secret information display unit. And a unit 36.
[0037]
(Input unit 31)
The input unit 31 is an input device such as a scanner, and receives the print document 20 printed on paper. When the print document 20 is made of black ink (single color) on a white paper surface, the print document 20 is captured as a gray image with multi-value gradation. Then, the watermarked document image shown in FIG. 3 is generated.
[0038]
(Secret information detector 32)
The secret information detection unit 32 performs a filtering process on the watermarked document image generated by the input unit 31 and detects an embedded signal. Then, the symbol is restored from the detected signal, and the embedded secret information is extracted. The secret information detected by the secret information detection unit 32 is in a state of being encrypted using the imprint feature data 17 as an encryption key.
[0039]
As such a watermark detection method, a method corresponding to the watermark embedding method in the secret information embedding device 10 described above can be adopted. In the present embodiment, the above-mentioned documents (Japanese Patent Application No. 2001-217758 “watermark information embedding device and watermark information detecting device”, and Japanese Patent Application No. 2002-177086 “watermark information embedding device and watermark information detecting device”) are disclosed. Technology can be adopted.
[0040]
(Seal area extraction unit 33)
When the printed document 20 is stamped, the stamp area extracting unit 33 extracts the stamped area. If the area (imprint area) where the seal is pressed in the print document 20 is known in advance, the imprint area can be easily extracted from the image of the print document 20 read by the input unit 31.
[0041]
On the other hand, if the area on the printed document 20 where the seal is pressed is not known in advance, the following processing is performed. The secret information 16 is embedded in the print document 20 as a digital watermark. Therefore, when a seal is pressed on an arbitrary area of the print document 20, the digital watermark in that area is substantially altered. Therefore, by adopting a technique that can detect such alteration (changed portion) of the digital watermark, it is possible to extract a region where a seal is pressed (imprint region).
[0042]
Techniques for detecting such digital watermark alteration are disclosed in, for example, a document (Japanese Patent Application No. 2002-003153 “Digital watermark embedding device, digital watermark detecting device, digital watermark embedding method, and digital watermark detecting method”). There is something. The digital watermark detection device disclosed in this document includes a character addition / tampering detection unit, and binarizes a document image in which confidential information is embedded with a predetermined threshold value, so that the pixel value of the character region is 0 and the background region is 0. A character area extracted image is created by setting the pixel value of the symbol unit to 1 and the pixel value of the area where the symbol unit cannot be detected is 0 in the document image in which the confidential information is embedded, and the pixel value of the area where the symbol unit can be detected is 1 It is characterized by detecting an alteration to a watermarked document image by creating an extracted image and comparing the character region extracted image with the symbol unit extracted image (generating a difference image). According to such a configuration, if there is a fraud such as adding an arbitrary character string to a printed document, tampering can be detected even without the original text of the document, and the tampering place can be specified.
[0043]
In addition, the following technology is described in the document as an application example. That is, in the electronic watermark detection device, it is possible to add a function of performing falsification detection by inserting additional information for falsification detection together with confidential information. That is, an embedding signal number detector for detecting the number of symbol units embedded when embedding confidential information in a document image, and a filter output value for calculating an output value of a predetermined filter for the input image and recording for each embedding area An optimum threshold determining unit that calculates an optimum threshold for detecting the number of symbol units embedded in the watermark image from a calculation value, a detection value of the embedded signal number detection unit, and a calculation value of the filter output value calculation unit. And a detection signal counting unit for detecting the number of symbol units actually embedded in the watermarked document image, and comparing the detection value of the embedded signal number detection unit with the count value of the signal detection counting unit, And a falsification determining unit that determines whether the watermarked document image has been falsified.
[0044]
According to this configuration, the document image is divided into several blocks, and by recording the number of symbol units embedded in each block, tampering can be detected in block units, and the tampering location can be specified. Become. Also, by recording the number of embedded signals, an optimum threshold value for signal detection or tampering detection can be obtained. In addition, if a printed document is fraudulent, such as adding a character string to a blank part or erasing an arbitrary character string with a correction fluid, tampering can be detected without the original text of the document. ， Also can identify the falsification place.
[0045]
The technique disclosed in the above document is merely an example for realizing the function of the seal stamp area extracting unit 33, and thus a more detailed description will be omitted. It goes without saying that other digital watermarking techniques may be employed to realize the function of the seal area extracting unit 33.
[0046]
(Imprint feature extraction unit 34)
The seal stamp feature extracting unit 34 calculates a seal imprint feature amount from the seal stamp extracted by the seal stamp region extracting unit 33, and generates seal stamp feature data in the same format as the seal stamp feature data 17 in the secret information embedding device 10. The details of the calculation of the imprint feature amount and the generation of the imprint feature data will be described later.
[0047]
(Decryption processing unit 35)
The decryption processing unit 35 decrypts the encrypted secret information 16 detected by the secret information detection unit 32 using the imprint feature data generated by the imprint feature extraction unit 34 as a decryption key.
[0048]
(Secret information display section 36)
The secret information display unit 36 displays the secret information 16 on a screen or the like when the decryption unit 35 correctly extracts the secret data.
[0049]
The secret information processing system 1 is configured as described above.
Next, the operation of the secret information processing system 1 will be described. First, the operation of the secret information embedding device 10 will be described.
[0050]
(Secret information embedding device 10)
FIG. 4 is a flowchart showing processing of the secret information embedding device.
The operation of the secret information embedding device 10 will be described with reference to FIG.
[0051]
(S101: Imprint feature data selection step)
First, an approver who is authorized to approve the disclosure of the secret information embedded in the print document 20 is determined, and the imprint feature data 17 of the approver is extracted. The identity of the approver may be kept secret or may be specified in the text of the printed document 20. When the approver is specified in the text of the print document 20, such a document may be registered in the document data 15 in advance.
[0052]
(S102: secret information encryption step)
Next, the secret information 16 to be embedded in the print document 20 is encrypted using the imprint characteristic data selected in step S101 as an encryption key.
[0053]
(S103: Document Data Imaging Step)
The document image forming unit 11 converts the document data 15 to be printed as the foreground of the print document 20 into an image to create a document image. FIG. 2 is an explanatory diagram illustrating an example of a document image. The toner is applied to the black pixel portions in the image and printed.
[0054]
(S104: Tamper detection data creation step)
Next, detection data used for extracting a seal imprint area in the seal stamp area extraction unit 33 of the secret information detection device 30 is created. That is, as described above, the seal region extracting unit 33 uses the technique disclosed in the document (Japanese Patent Application No. 2002-003153 “Digital watermark embedding device, digital watermark detecting device, digital watermark embedding method, and digital watermark detecting method”). When falsification is adopted, falsification detection data used to automatically extract the pressed area of the seal is created.
[0055]
However, if the area (imprint area) where the seal is pressed in the print document 20 is known in advance, this step S104 can be omitted. When the seal area extracting unit 33 of the secret information detecting device 30 employs a technique different from the above-described document to extract the seal imprint area, it creates detection data corresponding thereto.
[0056]
(S105: watermark data creation step)
Next, the watermark image forming unit 12 forms a watermark image of the encrypted secret information 16, and the watermarked image synthesizing unit 13 compares the document image formed by the document image forming unit 11 with the watermark image forming unit 12. Is superimposed on the watermark image formed by the above to create a watermarked document image. At this time, if necessary, the above-mentioned falsification detection data and other additional information are superimposed. FIG. 3 is an explanatory diagram showing an example of a watermarked document image in which secret information is embedded. The encrypted data and the tampering detection data are represented by a dot pattern and cannot be deciphered by human eyes.
[0057]
(S106: Watermark Printing Process)
The watermarked document image generated through the above steps is printed at the output unit 14.
[0058]
The operation of the secret information embedding device 10 has been described above. Next, the operation of the secret information detection device 30 will be described. Before describing the overall operation of the confidential information processing device 30, first, the operation of the seal stamp characteristic extracting unit 34 which is characteristic of the present embodiment will be described. FIG. 5 is a flowchart showing the imprint data extraction processing.
[0059]
(Step S201: Imprint area extraction step)
When the print document 20 is stamped, the seal imprint area is extracted by the seal area extraction unit 33. Then, an imprint image is generated. FIG. 6 is an explanatory diagram showing an example of the imprint image. This seal is “Oki” in a circle, representing the author of “Taro Oki”.
[0060]
(S202: Imprint area blocking step)
The seal stamp feature extraction unit 34 blocks the seal image extracted in step S201. FIG. 7 is an explanatory diagram showing an example in which the imprint image shown in FIG. 6 is divided into blocks. In this example, an example is shown in which the block is divided into n (n = 5 × 5 = 25) blocks B1 to Bn.
[0061]
(S203: Imprint characteristic data calculation step)
Next, the print feature extraction unit 34 calculates the feature amounts of the blocks divided in step S202, and generates imprint feature data. FIG. 8 is an explanatory diagram showing an example of generating imprint feature data from divided blocks. Here, as an example, the ratio of the black pixels to the area of each block is calculated as the feature amount of each block. Then, the concatenation of the feature values calculated for each block is defined as imprint feature data.
[0062]
For example, as shown in FIG. 8, the feature amount of the block B1 is calculated as “f”, the feature amount of the block B2 is “0”,..., And the feature amount of the block Bn is calculated as “0”. Then, “f0ac7a620b931f0” (in hexadecimal notation) in which the feature amounts of the blocks B1 to Bn are linked is set as imprint feature data. Note that the expression form of the imprint feature data needs to be the same as the expression format of the imprint feature data 17 in the secret information embedding device 10, and therefore, is not necessarily displayed in hexadecimal.
[0063]
The overall operation of the confidential information detection device 30 will be described based on the operation of the seal feature extraction unit 34 described above. FIG. 9 is a flowchart showing the processing of the secret information detecting device 30.
[0064]
First, the print document 20 is read by the input unit 31. FIG. 10 is an explanatory diagram illustrating an example of an image obtained by reading the print document 20 on which the seal has been pressed by the input unit 31. In this print document 20, a seal ("Oki" in a circle) of a person (Taro Okino) set as an approver is pressed.
[0065]
(S301: watermark data restoration step)
The secret information detection unit 32 detects watermark data from the image of the print document 20 captured by the input unit 31. For the detection of the watermark data, a method corresponding to the watermark embedding method in the secret information embedding device 10 described above can be adopted. In the present embodiment, the above-mentioned documents (Japanese Patent Application No. 2001-217758 “watermark information embedding device and watermark information detecting device”, and Japanese Patent Application No. 2002-177086 “watermark information embedding device and watermark information detecting device”) are disclosed. Technology can be adopted. The data detected thereby are (1) encrypted secret information 16, (2) falsification detection data, and (3) other data.
[0066]
(S302: tampering detection step)
Next, a seal stamp area is extracted by the seal stamp area extracting unit 33. If the area (imprint area) where the seal is pressed in the print document 20 is known in advance, the imprint area can be easily extracted from the image of the print document 20 read by the input unit 31. If the area (imprint area) where the seal is pressed in the print document 20 is not known in advance, the above-mentioned document (Japanese Patent Application No. 2002-003153, entitled “Digital watermark embedding device, digital watermark detecting device, digital watermark embedding method, , Digital watermark detection method ”), a technique for detecting alteration of a digital watermark.
[0067]
(S303: alteration presence / absence determination step)
If a seal is pressed on the printed document 20, that part is an area that did not exist as character information of the original document data, and is detected as a newly added falsified area. If the tampered area is not detected, it is determined that the seal has not been pressed, and the process is stopped without decrypting the secret information 16.
[0068]
(S304: Imprint image retrieval step)
If it is determined in step S303 that the seal is falsified, that is, if the seal is pressed on the print document 20, the seal imprint area is cut out and the seal imprint image is extracted. A binary image is generated by separating a background area including a digital watermark (dot pattern) from the foreground of the imprint using an appropriate threshold value. It is assumed that the extracted imprint image has been subjected to normalization processing such as rotation correction.
[0069]
(S305: Imprint feature data creation step)
According to the method described with reference to FIGS. 5 to 8, imprint feature data is created from the imprint image extracted in step S304. The creation of the imprint feature data is as described above with reference to FIGS.
[0070]
(S306: encryption information decryption step)
The encrypted secret information 16 is decrypted using the imprint feature data created in step S305. At this time, it is determined whether or not the secret information 16 has been correctly decrypted (step S307). If the secret information 16 has not been correctly decrypted, the imprint characteristic data is incorrect, that is, a stamp different from the set approver's seal is pressed. And the process ends.
[0071]
(S308: secret information display step)
In step S307, if the secret information 16 has been correctly decrypted, that is, if the correct approval mark has been pressed, the secret information 16 is displayed on the screen in the secret information display unit 36.
[0072]
As described above, according to the present embodiment, the secret information is encrypted using the imprint image data 17 of the approver who is authorized to approve the release of the secret information as the encryption key. Only when the approval mark of the approver is given to the print document (watermarked document) of the paper medium, the secret information is decrypted using the approval mark as a decryption key and the secret information is displayed. As described above, since the physical approval method of making an approval stamp on a paper medium is used for decryption of digital encryption, there is no need to manage an encryption key (for example, a password) for disclosing secret information. Further, since the approval mark given to the paper medium means that the confidential information can be disclosed, it is easy to distinguish a document in which the confidential information is disclosed from a document in which the confidential information is not disclosed. .
[0073]
The preferred embodiments of the secret information processing system, the secret information embedding device, the secret information detection device, the secret information embedding method, and the secret information detection method according to the present invention have been described with reference to the accompanying drawings. It is not limited to such an example. It is obvious that a person skilled in the art can conceive various changes or modifications within the scope of the technical idea described in the claims, and those changes naturally fall within the technical scope of the present invention. It is understood to belong.
[0074]
For example, in the above-described embodiment, the imprint of the approver has been described as an example of the unique information unique to the approver who has been authorized to approve the release of the secret information. However, the present invention is not limited to this. For example, a signature of the approver, which is hard to be imitated by others and is invariant, can be used as the approver's unique information in the present invention as long as it can be used to identify the user.
[0075]
Further, in the above-described embodiment, a case has been described in which confidential information is embedded in a print document by using a digital watermark technique, but the present invention is not limited to this. If the position of the seal is predetermined, the encrypted secret information may be replaced with a barcode or a two-dimensional barcode.
[0076]
Further, in the above embodiment, a case has been described where a watermarked document image is created by superimposing a document image and a watermark image. However, the present invention is not limited to this. For example, a dot pattern is directly added to a document image. It is also possible.
[0077]
【The invention's effect】
As described above, according to the present invention, secret information is encrypted using unique information unique to an approver who has been authorized to approve disclosure of secret information as an encryption key. Only when the printed document (watermarked document) of the paper medium is given unique information unique to the approver (for example, an approval mark or a signature), the secret information is decrypted using the unique information as a decryption key. , To display confidential information. As described above, since the physical approval method of performing an approval stamp or signature on a paper medium is used for decryption of digital encryption, it is not necessary to manage an encryption key (for example, a password) for disclosing secret information. Furthermore, the fact that the approval mark or signature is given to the paper medium means that the confidential information can be made public. Easy.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a secret information processing system.
FIG. 2 is an explanatory diagram illustrating an example of a document image.
FIG. 3 is an explanatory diagram illustrating an example of a watermarked document image in which secret information is embedded.
FIG. 4 is a flowchart showing processing of the secret information embedding device.
FIG. 5 is a flowchart showing a seal imprint data extraction process.
FIG. 6 is an explanatory diagram showing an example of a seal image.
FIG. 7 is an explanatory diagram showing an example in which the imprint image shown in FIG. 6 is divided into blocks.
FIG. 8 is an explanatory diagram showing an example of generating imprint feature data from divided blocks.
FIG. 9 is a flowchart showing processing of the secret information detection device.
FIG. 10 is an explanatory diagram illustrating an example of an image obtained by reading a print document on which a seal has been pressed by an input unit;
[Explanation of symbols]
1 secret information processing system
10 Secret information embedding device
11 Document image forming unit
12 watermark image forming unit
13 Document Image Synthesis Unit with Watermark
14 Output section
15 Document data
16 confidential information
17 Imprint feature data
20 printed documents (paper)
30 Secret information detection device
31 Input section
32 Secret information detector
33 Seal area extraction unit
34 Imprint Feature Extraction Unit
35 decryption processing unit
36 Secret information display section

Claims (18)

Exchange of secret information using a document as a medium between a secret information embedding device that embeds secret information in a document using a digital watermark and a secret information detection device that detects secret information embedded in the document using a digital watermark Confidential information processing system,
The secret information embedding device comprises:
A document image forming unit for creating a document image based on the document data;
A unique information database that manages unique information unique to an approver who is authorized to approve disclosure of confidential information;
A watermark image forming unit that encrypts the secret information using the unique information as an encryption key and forms a watermark image based on the encrypted secret information;
An output unit that outputs a watermarked document based on the document image and the watermark image;
With
The secret information detecting device comprises:
An input unit that receives the watermarked document and generates a watermarked document image by superimposing the document image and the watermark image;
A secret information detection unit that detects the encrypted secret information from the watermarked document image;
When the watermarked document has been given unique information unique to an approver who has been authorized to approve publication of the secret information, a unique information extracting unit for extracting the unique information;
A decryption processing unit that decrypts the secret information using the unique information as a decryption key;
A secret information display unit for displaying the secret information;
A secret information processing system, comprising: 2. The secret information processing system according to claim 1, wherein the unique information is information on a seal imprint of a seal owned by the approver. 2. The secret information processing system according to claim 1, wherein the unique information is information on a signature of the approver. The secret information processing system according to claim 1, wherein the unique information is irreversible that cannot identify the approver. The secret information processing system according to any one of claims 1 to 4, wherein the unique information is provided to a predetermined area of the watermarked document. The secret information detecting device comprises:
A unique information area extraction unit that extracts an area of the watermarked document to which the unique information is given;
The secret information processing system according to claim 1, wherein the unique information extracting unit extracts the unique information from an area extracted by the unique information area extracting unit. 7. The method according to claim 6, wherein the unique information area extraction unit extracts a region of the watermarked document to which the unique information is given by detecting a changed portion of the watermarked document. Described secret information processing system. A secret information embedding device for embedding secret information in a document using a digital watermark,
A document image forming unit for creating a document image based on the document data;
A unique information database that manages unique information unique to an approver who is authorized to approve disclosure of confidential information;
A watermark image forming unit that encrypts the secret information using the unique information as an encryption key and forms a watermark image based on the encrypted secret information;
An output unit that outputs a watermarked document based on the document image and the watermark image;
A secret information embedding device, comprising: 9. The secret information embedding device according to claim 8, wherein the unique information is information on a seal imprint of a seal stamp owned by the approver. 9. The secret information embedding device according to claim 8, wherein the unique information is information on a signature of the approver. 9. The secret information embedding device according to claim 8, wherein the unique information is irreversible that cannot identify the approver. The secret information embedding device according to claim 8, wherein the unique information is provided to a predetermined area of the watermarked document. A secret information detection device for detecting secret information embedded in a document using a digital watermark,
An input unit for receiving a watermarked document and generating a watermarked document image;
A secret information detection unit for detecting encrypted secret information from the watermarked document image;
When the watermarked document has been given unique information unique to an approver who has been authorized to approve publication of the secret information, a unique information extracting unit for extracting the unique information;
A decryption processing unit that decrypts the secret information using the unique information as a decryption key;
A secret information display unit for displaying the secret information;
A confidential information detection device comprising: A unique information area extraction unit that extracts an area of the watermarked document to which the unique information is given;
14. The secret information detecting apparatus according to claim 13, wherein the unique information extracting unit extracts the unique information from the area extracted by the unique information area extracting unit. 15. The method according to claim 14, wherein the unique information area extraction unit extracts an area of the watermarked document to which the unique information is given by detecting a changed portion of the watermarked document. Described secret information detection device. A secret information embedding method for embedding secret information in a document using a digital watermark,
A document image forming step of creating a document image based on the document data;
A watermark image forming step of encrypting the secret information using unique information unique to an approver authorized to approve disclosure of the secret information as an encryption key and forming a watermark image based on the encrypted information;
An output step of outputting a watermarked document based on the document image and the watermark image;
A method for embedding confidential information, comprising: A secret information detection method for detecting secret information embedded in a document using a digital watermark,
An input step of receiving a watermarked document and generating a watermarked document image;
A secret information detecting step of detecting encrypted secret information from the watermarked document image;
When the watermarked document has been given unique information unique to an approver who has been authorized to approve publication of the secret information, a unique information extracting step of extracting the unique information;
A decryption processing step of decrypting the secret information using the unique information as a decryption key;
A secret information display step of displaying the secret information;
A method for detecting confidential information, comprising: A unique information area extracting step of extracting an area of the watermarked document to which the unique information is given;
18. The secret information detecting method according to claim 17, wherein the unique information extracting step includes a step of extracting the unique information from the area extracted in the unique information area extracting step.

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