JP2004072169A - Image encryption/decryption apparatus, system, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image encryption/decryption apparatus that encrypts image data in a form of much more keeping an outline of an image while protecting image contents so as to more easily adjust the outline keeping level. <P>SOLUTION: An encryption means 20 in the image encryption apparatus 1 encrypts other data than outline data not to be encrypted whereby the outline of an image can be grasped in image data P acquired by an image data acquisition means 10, and a partial encryption data generating means 30 generates partially encrypted data C including outline data P1, encrypted data P2' and lock data L corresponding to key data K used to decrypt the encrypted data P2'. A partially encrypted data acquisition means 40 acquires partially encrypted data C, and a lock data extract means 60 extracts the lock data L from the partially encrypted data C. A decryption means 70 decrypts the encrypted data P2' only when the key data K acquired by a key data acquisition means 50 are true key data corresponding to the extracted lock data L so as to display an image represented by the original image data P. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image encryption / decryption device, system, and program for protecting image data.
[0002]
[Prior art]
In recent years, digital data is frequently handled in various fields due to improvements in digital technology and the spread of standards. In particular, the distribution and sale of data via a server on the Internet, media, and the like are actively performed.
[0003]
As one of the data sales formats, providers with images and CG (computer graphics) content protect the contents while presenting the outline of the image to the consumer, and the consumer views the outline of the image. There is a format in which the purchase procedure is performed if the user likes it, and the provider sends the customer information regarding the data and the procedure for removing the protection of the image after confirming the completion of the purchase procedure of the consumer.
[0004]
At this time, what is particularly important in order to motivate consumers to purchase is the level of retention of the outline in the presentation of images. For example, if the retention level of the summary is low and the content is hardly understood, the consumer will not know whether it is what they want, so there is no willingness to purchase, and conversely, the summary retention level is high and most can be grasped. If so, you can enjoy it as it is without having to purchase it. Therefore, when presenting an outline of an image, it is necessary to balance the above balance.
[0005]
By the way, as a technique for protecting an image, various techniques have been proposed so far, for example, image data is encoded using a quantization table and then provided in combination with a quantization table for disturbance. There is a technique (Japanese Patent Laid-Open No. 10-304206) that prevents encoded data from being correctly decoded unless a true quantization table is obtained.
[0006]
[Problems to be solved by the invention]
However, according to the conventional method, since the entire image data is encrypted and the original image data does not remain, the encrypted data has a relatively low level of outline of the image and the content is Because it was difficult to grasp, sufficient appeal to consumers was not made. Further, since the entire image data is encrypted, there is a problem that it is difficult to adjust the retention level of the outline of the image, and it is difficult to adjust the retention level of the outline of the presented image to a desired level.
[0007]
The present invention has been made in view of the above circumstances, and image data can be encrypted in a form in which the outline of the image is more retained while protecting the content of the image, and the outline retention level is adjusted. It is an object of the present invention to provide an image encryption / decryption device, system, and program that can make the process easier.
[0008]
[Means for Solving the Problems]
The first image encryption / decryption system according to the present invention is an image encryption / decryption system comprising an image encryption device for encrypting image data and an image decryption device for decrypting the encrypted data. In the image encryption apparatus, the image data acquisition means for acquiring the image data, the encryption means for encrypting other data, leaving the outline data that can grasp the outline of the image among the acquired image data, An image decryption apparatus comprising: partially encrypted data generation means for generating partially encrypted data including summary data, encrypted data, and lock data corresponding to key data used for decryption of the encrypted data The partial encrypted data acquisition means for acquiring the generated partial encrypted data, the key data acquisition means for acquiring the key data, and the lock data is extracted from the acquired partial encrypted data. Lock data extracting means, and decryption means capable of decrypting encrypted data only when the acquired key data is true key data corresponding to the extracted lock data. It is characterized by that.
[0009]
A first image encryption apparatus according to the present invention includes an image data acquisition unit that acquires image data, and encryption that encrypts other data while leaving outline data that can grasp an outline of the image among the acquired image data. And partially encrypted data generating means for generating partially encrypted data including summary data, encrypted data, and lock data corresponding to key data used for decryption of the encrypted data. This is used for the first image encryption / decryption system.
[0010]
A first image decryption apparatus according to the present invention includes a partial encrypted data acquisition unit that acquires generated partial encrypted data, a key data acquisition unit that acquires key data, and a lock from the acquired partial encrypted data. Lock data extraction means for extracting data, and decryption means capable of decrypting encrypted data only when the acquired key data is true key data corresponding to the extracted lock data Are used for the first image encryption / decryption system.
[0011]
Here, “summary data” means a part of data in image data for displaying an image to the extent that the outline or color of the object represented in the image can be grasped. It is.
[0012]
“Key data” and “lock data” are used to protect and release image data, and key data and lock data always exist in pairs. In the image decryption apparatus, the encrypted data is decrypted only when the true key data corresponding to the lock data included in the partially encrypted data is acquired.
[0013]
The pair of key data and lock data may be different for each image data, or the same data may be used for a plurality of image data belonging to a predetermined group.
[0014]
Also, the key data and lock data may be prepared as data used for computation of encryption and decryption processing, or as data for confirming only matching, not used for computation of encryption and decryption processing. You may prepare.
[0015]
In the first image encryption device, the outline data may be data corresponding to a low frequency component or a high frequency component of an image represented by the image data, and a representative contour of the image represented by the image data. It may be data corresponding to.
[0016]
The data corresponding to the low-frequency component of the image is data representing an image with a smooth gradation change in a raster image, such as a so-called blurred image. For example, the image data is divided into several frequency bands. In the case of data used in progressive JPEG, progressive GIF, etc., where the clarity of the image differs depending on which frequency band is displayed when it is divided into components and displayed, in the image data Data representing a relatively low frequency component.
[0017]
Further, the data corresponding to the high-frequency component is data representing an image in which only a so-called contour portion of an object is conspicuous in a raster image, and the data used in the above-described progressive JPEG or the like. In this case, it can be data representing a relatively high frequency component in the image data.
[0018]
The data corresponding to the typical contour of the image is data representing a rough contour in the image data composed of vector data representing the contour of the object as seen in CG (computer graphics) or the like. Yes, for example, when the image data is composed of data including a wire frame representing the contour of an object, it can be data corresponding to a baseline (outer frame portion or skeleton portion) in the wire frame. . The wire frame may be curved or may be a polygonal line.
[0019]
A second image encryption / decryption system according to the present invention is an image encryption / decryption system comprising an image encryption device for encrypting image data and an image decryption device for decrypting the encrypted data. The image encryption apparatus includes an image data acquisition unit that acquires image data, a reduced image data generation unit that generates reduced image data representing a reduced image of the image represented by the image data based on the acquired image data, and Generates partially encrypted data including encryption means for encrypting acquired image data, reduced image data, encrypted data, and lock data corresponding to key data used for decrypting the encrypted data A partial encrypted data generation means, wherein the image decryption device acquires the partial encrypted data generated and a key for acquiring the key data Data acquisition means, lock data extraction means for extracting lock data from the acquired partial encrypted data, and only when the acquired key data is true key data corresponding to the extracted lock data, And a decryption unit capable of decrypting the encrypted data.
[0020]
The “reduced image” means an image whose size is reduced to such an extent that the outline can be grasped by reducing the number of pixels but the details cannot be sufficiently seen by reducing the pixels.
[0021]
Note that each means of the present invention may be supplied as a program for causing a computer to execute the means.
[0022]
Note that the image data may be not only data representing a still image but also data representing a moving image, and may further include sound information representing sound.
[0023]
【The invention's effect】
In a first image encryption / decryption system according to the present invention, an image encryption apparatus leaves summary data that can grasp an outline of an image among acquired image data, encrypts other data, Generate partially encrypted data including encrypted data and lock data corresponding to key data used for decryption of the encrypted data, and the image decryption device extracts the lock data from the acquired partially encrypted data. The encrypted data is decrypted only when the extracted and acquired key data is the true key data corresponding to the extracted lock data. Therefore, in the image encryption device, although a part of the image data is encrypted, the summary data of the image data is not encrypted and remains as the original data. Compared to data obtained by encrypting the entire image data, the outline of the image is more retained, and an image closer to the original image can be displayed. Further, the adjustment of the image outline holding level can be realized by adjusting the range of the image data to be retained as the outline data, so that fine adjustment can be easily performed.
[0024]
In the second image encryption / decryption system according to the present invention, the image encryption device generates reduced image data representing a reduced image of the image represented by the acquired image data, encrypts the acquired image data, Partially encrypted data including reduced image data, encrypted data, and lock data corresponding to key data used for decryption of the encrypted data is generated, and the image decryption apparatus acquires the partially encrypted data. The lock data is extracted from the data, and the encrypted data is decrypted only when the acquired key data is the true key data corresponding to the extracted lock data. Therefore, the generated partially encrypted data includes reduced image data representing a reduced image of the image represented by the image data so that the outline of the image can be grasped but the details cannot be sufficiently seen. Since the image data is a reduced version of the original image, the outline of the image is more retained as compared with the data obtained by encrypting the entire image data, and can be displayed in a state close to the original image. Further, the adjustment of the level of the outline of the image can be realized by adjusting the degree of image reduction, so that fine adjustment can be easily performed.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an image encryption / decryption system according to the present invention will be described below with reference to the drawings.
[0026]
First, a first embodiment to which the first image encryption / decryption system according to the present invention is applied will be described. FIG. 1 is a schematic block diagram of an image encryption / decryption system according to the first embodiment.
[0027]
The image encryption / decryption system according to the present embodiment includes an image encryption device 1 that encrypts an image and an image decryption device 2 that decrypts encrypted data. The image encryption device 1 includes an image data acquisition unit 10 that acquires the image data P, and an encryption unit that encrypts other data while retaining the outline data from which the outline of the image can be grasped. 20, summary data P1 (unencrypted data), data P2 ′ (encrypted data) encrypted by the encryption means 20, and lock data L corresponding to key data K used for decrypting the encrypted data, And partially encrypted data generating means 30 for generating partially encrypted data C including The image decryption apparatus 2 also includes a partial encrypted data acquisition unit 40 that acquires the partial encrypted data C, a key data acquisition unit 50 that acquires the key data K, and lock data from the acquired partial encrypted data C. Lock data extraction means 60 for extracting L, and decryption means 70 for decrypting the encrypted data when the acquired key data K is true key data K corresponding to the extracted lock data L; When the encrypted data is not decrypted, only the unencrypted data is displayed. When the encrypted data is decrypted, the display unit 80 displays the image represented by the original image data P. .
[0028]
The display unit 80 is not an essential component in the image encryption / decryption system according to the present invention.
[0029]
The encryption device 1 has a provider that distributes the image data P for a fee, and stores the partially encrypted data C generated by the encryption device 1 on a server connected to the Internet. A personal computer on which a program for executing the decoding process and the display process is installed is used as the image decoding apparatus 2, and the personal computer is connected to a server via the Internet so that an outline of an image provided by the provider can be viewed. It is like that.
[0030]
In the present embodiment, the image data P is a method in which an image is divided into components for each frequency band, and the clarity of the image varies depending on which frequency band is displayed. It is assumed that the data is used in (for example, progressive JPEG), and the above-mentioned “summary data that can grasp the outline of the image” is the low frequency component of the image.
[0031]
The key data K and the lock data L are both password numbers, and the image decryption apparatus 2 performs a process of decrypting the encrypted data if both password numbers meet a predetermined rule. Assume that the entire image data P can be displayed.
[0032]
As shown in FIG. 2, the partially encrypted data C is composed of a header, non-encrypted data, and encrypted data. In this embodiment, the partially encrypted data C includes data representing a low-frequency component, encrypted data Data in which high-frequency components are encrypted as encrypted data, and lock data L is added to the header.
[0033]
Next, the operation of the first image encryption / decryption system according to this embodiment will be described.
[0034]
First, processing on the provider side will be described. In the image encryption device 1, the image data P is acquired by the image data acquisition unit 10, the high frequency component is encrypted while the low frequency component of the image data P is left as it is by the encryption unit, and further the partially encrypted data generation unit 30. Displays only the outline of the image including the low-frequency component that is non-encrypted data, the data that is encrypted with the high-frequency component that is encrypted data, and the header that is given the password as the lock data L Possible partial encrypted data C is generated. The provider stores the generated partially encrypted data C on the server in a state where the consumer can view it.
[0035]
Next, processing on the consumer side will be described. The consumer connects his / her personal computer as the image decoding device 2 to the provider's server via the Internet. In the image decryption apparatus 2 (personal computer), the partial encrypted data C provided by the provider is obtained by the partial image data obtaining unit 40, and the non-encrypted data of the partially encrypted data C is displayed on the display screen of the personal computer. The consumer can view the outline of the image. The consumer performs a purchase procedure if there is an image that he / she wishes to purchase among the browsed images. Upon confirming the purchase procedure of the consumer, the provider obtains a code number (key data K) for decrypting the encrypted data corresponding to the code number (lock data L) included in the partially encrypted data C. Record it on paper media and mail it to consumers. The consumer inputs the personal identification number (key data K) sent from the provider on the personal identification number input screen of the personal computer, and the personal identification number as the key data K is acquired by the key data acquisition means 50. If the code number as the lock data L included in the partially encrypted data C is extracted by the lock data extraction means 60 and the acquired code number is true key data K corresponding to the extracted lock data L, decryption is performed. The encrypted data in the partially encrypted data C is decrypted by the converting means 70, and the image represented by the image data P can be completely displayed on the screen of the personal computer. If the password is not entered or if the entered password is incorrect, the encrypted data is not decrypted and a complete image cannot be displayed.
[0036]
FIG. 3A is an image before decryption represented by the partially encrypted data C according to the present embodiment, and FIG. 3B is a diagram illustrating an image after decryption. In the image before decryption, the low-frequency component is displayed as unencrypted data in the original data, so the contour is blurred, but the contour position can be specified within a certain range. Compared to, the outline is more understandable.
[0037]
Thus, in the partially encrypted data C, the low frequency component of the image data P is left as the original data as non-encrypted data, and only the high frequency component of the image data P is encrypted as encrypted data. Therefore, before decryption, only the low-frequency component of the unencrypted data can be displayed, and an image with a blurred outline is displayed on the screen. However, since the low frequency component is a part of the original image data, it can be viewed in a state close to the original image compared to the conventional method of encrypting the entire image data, and the consumer is more willing to purchase. It has an arousing effect. In addition, since the general retention level can be adjusted depending on which frequency band component the non-encrypted data is expanded to, finer adjustment is possible.
[0038]
In addition, as summary data, a high frequency component may be left contrary to the above-described low frequency component, and in this case, only an outline portion of an object or the like is conspicuous. Further, the image data P may be data in other formats, for example, data representing a vector image, and outline data to be left as unencrypted data may be a wire frame baseline indicating an outline of the outline, A curved line or a polygonal line can be considered. FIG. 4 shows an example of an image represented by the partially encrypted data C when the outline data is a baseline of a curved wire frame. FIG. 5 shows a partial encryption when the outline data is a baseline of a polygonal wire frame. An example of an image represented by data C is shown.
[0039]
When the provider sends the personal identification number as the key data K to the consumer, if the security can be sufficiently secured, the personal identification number may be transmitted to the consumer's email address by e-mail or the like.
[0040]
The pair of key data and lock data may be different for each image data P, or the same data is used for a plurality of image data belonging to a predetermined group, and the consumer You may make it possible to view an image freely within a group.
[0041]
Further, the key data K and the lock data L may be prepared as data used for the operations of the encryption and decryption processing, or are not used for the operations of the encryption and decryption processing, and only a simple matching is confirmed. It may be prepared as data.
[0042]
The configuration of the partially encrypted data C is not limited to that shown in the present embodiment.
[0043]
As means for displaying the partially encrypted data C, an image represented by the unencrypted data of the partially encrypted data C is displayed, and if the true key data is acquired, the decrypted data is also included. In other words, it is conceivable to use a dedicated viewer that displays an image represented by all image data. However, when a general viewer can be used, such a method may be used.
[0044]
Next, a second embodiment to which the second image encryption / decryption system according to the present invention is applied will be described. FIG. 6 is a schematic block diagram of an image encryption / decryption system according to the second embodiment.
[0045]
As in the first embodiment, the image encryption / decryption system according to the present embodiment does not encrypt the other data while leaving the summary data from which the outline of the image can be grasped. When the consumer purchases a reduced image of the image represented by the image data P to be sold as an image presented to show the image, the encrypted image data P can be decrypted.
[0046]
Therefore, the image encryption device 1 generates the reduced image data P0 that represents the reduced image of the image represented by the image data P based on the acquired image data P and the image data acquisition unit 10 that acquires the image data P. Data generation means 15, encryption means 20 for encrypting the acquired image data P, reduced image data P0, encrypted data P ', and key data K used for decryption of the encrypted data P' And partially encrypted data generating means 30 for generating partially encrypted data C including the lock data L corresponding to. The image decoding device 2 has the same configuration as that of the first embodiment.
[0047]
Next, the operation of the image encryption / decryption system according to the present embodiment will be described.
[0048]
First, processing on the provider side will be described. In the image encryption device 1, the image data P is acquired by the image data acquisition unit 10, and the reduced image data generation unit 15 reduces the number of pixels of the image represented by the image data P based on the acquired image data P. Reduced image data P0 representing a reduced image is generated, the image data P is encrypted by the encryption unit 20, and further, the partially encrypted data generation unit 30 uses the reduced image data P0 which is non-encrypted data and the encrypted data. Partially encrypted data C is generated, which includes an encrypted data P ′ of a certain image data P and a header to which a personal identification number as a lock data L is assigned and can display an outline of the image as a reduced image. The provider stores the generated partially encrypted data C on the server in a state where the consumer can view it.
[0049]
Next, processing on the consumer side will be described. The consumer connects his / her personal computer as the image decoding device 2 to the provider's server via the Internet. In the image decryption apparatus 2 (personal computer), the partial encrypted data C provided by the provider is obtained by the partial image data obtaining means 40, and the reduced image that is the non-encrypted data of the partially encrypted data C is displayed on the screen of the personal computer. P0 is displayed by the display means 80, and the consumer can view the outline of the image through the reduced image. The consumer performs a purchase procedure if there is an image that he / she wishes to purchase among the browsed images. Upon confirming the purchase procedure of the consumer, the provider obtains a code number (key data K) for decrypting the encrypted data corresponding to the code number (lock data L) included in the partially encrypted data C. Record it on paper media and mail it to consumers. The consumer inputs the personal identification number (key data K) sent from the provider on the personal identification number input screen of the personal computer, and the personal identification number as the key data K is acquired by the key data acquisition means 50. If the code number as the lock data L included in the partially encrypted data C is extracted by the lock data extraction means 60 and the acquired code number is true key data K corresponding to the extracted lock data L, decryption is performed. The encrypted data of the encrypted data C is decrypted by the converting means 70, and the image represented by the image data P can be displayed in the original size on the screen of the personal computer. If the password is not entered or if the entered password is incorrect, the encrypted data is not decrypted and a complete image cannot be displayed.
[0050]
FIG. 7A shows an example of an image before decryption (reduced image) represented by the partially encrypted data C according to the method of the present embodiment, and FIG. 7B shows an example of an image after decryption (original image). FIG. In the image before decryption, a reduced image obtained by reducing the original image is displayed as non-encrypted data, so although details are not clear, the outline and color can be understood almost completely, and the outline is better than the conventional method It is a description that can be grasped.
[0051]
Thus, the partially encrypted data C is a non-encrypted data that is a reduced image of the image represented by the image data P, and the image data P is encrypted as encrypted data. Only a reduced image of the encrypted data can be displayed, and an image with no details is displayed on the screen. However, since the reduced image data is simply reduced in size by reducing the number of pixels of the image represented by the original image data, it can be viewed in a state closer to the original image than in the conventional method in which the entire image data is encrypted. This is effective in urging consumers to purchase more. In addition, since the outline holding level can be adjusted depending on how much the image is reduced, finer adjustment is possible.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an image encryption / decryption system according to a first embodiment.
FIG. 2 is a diagram showing a format of partially encrypted data C.
FIG. 3 shows an image before decryption and an image after decryption represented by the partially encrypted data C according to the first embodiment.
FIG. 4 is an image represented by partially encrypted data C when the outline data is a baseline of a curved wire frame.
FIG. 5 shows an image represented by partially encrypted data C when the outline data is a baseline of a polygonal wire frame.
FIG. 6 is a schematic block diagram of an image encryption / decryption system according to a second embodiment.
FIG. 7 shows an image before decryption (reduced image) and an image after decryption (original image) of the image represented by the partially encrypted data C according to the second embodiment.
[Explanation of symbols]
1 Image encryption device
2 Image decoding device
10 Image data acquisition means
15 Reduced image data generation means
20 Encryption means
30 Partially encrypted data generation means
40 Partially encrypted data acquisition means
50 Key data acquisition means
60 tablet data extraction means
70 Decryption means

Claims (14)

In an image encryption / decryption system comprising an image encryption device for encrypting image data and an image decryption device for decrypting encrypted data,
The image encryption device is
Image data acquisition means for acquiring the image data;
Among the acquired image data, leaving the summary data that can grasp the summary of the image, encryption means for encrypting other data,
Partially encrypted data generating means for generating partially encrypted data including the summary data, the encrypted data, and lock data corresponding to key data used to decrypt the encrypted data ,
The image decoding device comprises:
Partial encrypted data acquisition means for acquiring the generated partial encrypted data;
Key data acquisition means for acquiring the key data;
Lock data extraction means for extracting the lock data from the acquired partial encrypted data;
Decryption means capable of decrypting the encrypted data only when the acquired key data is true key data corresponding to the extracted lock data. An image encryption / decryption system. Image data acquisition means for acquiring the image data;
Among the acquired image data, leaving the summary data that can grasp the summary of the image, encryption means for encrypting other data,
Partially encrypted data generating means for generating partially encrypted data including the summary data, the encrypted data, and lock data corresponding to key data used to decrypt the encrypted data The image encryption apparatus used for the image encryption / decryption system according to claim 1. Partial encrypted data acquisition means for acquiring the generated partial encrypted data;
Key data acquisition means for acquiring the key data;
Lock data extraction means for extracting the lock data from the acquired partial encrypted data;
Decryption means capable of decrypting the encrypted data only when the acquired key data is true key data corresponding to the extracted lock data. An image decryption apparatus used in the image encryption / decryption system according to claim 1. 3. The image encryption apparatus according to claim 2, wherein the summary data is data corresponding to a low frequency component of an image represented by the image data. 3. The image encryption apparatus according to claim 2, wherein the summary data is data corresponding to a high frequency component of an image represented by the image data. 3. The image encryption apparatus according to claim 2, wherein the summary data is data corresponding to a typical contour of an image represented by the image data. In an image encryption / decryption system comprising an image encryption device for encrypting image data and an image decryption device for decrypting encrypted data,
The image encryption device is
Image data acquisition means for acquiring the image data;
Reduced image data generation means for generating reduced image data representing a reduced image of an image represented by the image data based on the acquired image data;
Encryption means for encrypting the acquired image data;
Partial encrypted data generation means for generating partial encrypted data including the reduced image data, the encrypted data, and lock data corresponding to key data used for decryption of the encrypted data; Prepared,
The image decoding device comprises:
Partial encrypted data acquisition means for acquiring the generated partial encrypted data;
Key data acquisition means for acquiring the key data;
Lock data extraction means for extracting the lock data from the acquired partial encrypted data;
Decryption means capable of decrypting the encrypted data only when the acquired key data is true key data corresponding to the extracted lock data. An image encryption / decryption system. The procedure to acquire image data,
Among the acquired image data, leaving the summary data that can grasp the summary of the image, the procedure of encrypting other data,
An image encryption process including: a procedure for generating partially encrypted data including the summary data, the encrypted data, and lock data corresponding to key data used for decrypting the encrypted data; A program that causes a computer to execute. Among the image data, partially encrypted data consisting of the summary data and the encrypted data, obtained by encrypting other data, leaving summary data that can grasp the summary of the image, A procedure for obtaining partially encrypted data including lock data corresponding to key data used for decryption of encrypted data;
Obtaining the key data;
A procedure for extracting the lock data from the partially encrypted data obtained;
For causing a computer to execute an image decryption process including a procedure for decrypting the encrypted data only when the acquired key data is true key data corresponding to the extracted lock data. program. 9. The program according to claim 8, wherein the summary data is data corresponding to a low frequency component of an image represented by the image data. 9. The program according to claim 8, wherein the summary data is data corresponding to a high frequency component of an image represented by the image data. 9. The program according to claim 8, wherein the summary data is data corresponding to a representative contour of an image represented by the image data. The procedure to acquire image data,
Generating reduced image data representing a reduced image of the image represented by the image data based on the acquired image data;
A procedure for encrypting the image data;
An image encryption process including a procedure for generating partially encrypted data including the reduced image data, the encrypted data, and lock data corresponding to key data used for decryption of the encrypted data A program that causes a computer to execute. Reduced image data representing a reduced image of an image represented by the image data, encrypted data obtained by encrypting the image data, and lock corresponding to key data used for decrypting the encrypted data To obtain partially encrypted data including data,
Obtaining the key data;
A procedure for extracting the lock data from the partially encrypted data obtained;
For causing a computer to execute an image decryption process including a procedure for decrypting the encrypted data only when the acquired key data is true key data corresponding to the extracted lock data. Program.

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