JP2002010044A - Memory card, image forming apparatus, image forming method, and storage medium - Google Patents

Abstract

(57) [Problem] To prevent falsification of image file data created in an image forming apparatus and stored in a memory card, thereby improving the reliability of the image file data. When storing image file data created by an image forming apparatus in a memory card, a message digest value of the image file data is calculated using a one-way function, and the message digest value is calculated using a secret key. And storing the signature in the memory card together with the image file data, thereby making it difficult to falsify the signature and improving the reliability of the image file data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a memory card, an image forming apparatus, an image forming method, and a storage medium.

[0002]

2. Description of the Related Art Conventionally, a method of storing image file data created by an image forming apparatus such as an electronic still camera in a memory card has been used. If the image file data is to be printed using the memory card, a personal computer (hereinafter abbreviated as PC) connected to the printer or the printer itself may be provided with an interface (hereinafter, I / O) capable of accessing the memory card.
(Abbreviated as F), printing can be performed by connecting the memory card.

If the image file data is to be transferred to a personal computer, an electronic organizer, or the like, the memory card is connected to a transfer device having an I / F that can access the memory card.
Transfer of image file data can be easily performed.

[0004]

However, the conventional storage method has the following problems. That is, since the image file data stored in the memory card is electronic data, copying is easy. Therefore, there has been a problem that illegal duplication, unauthorized use, falsification, etc. are performed. Therefore, it has been necessary to prove that the image file data stored in the memory card is not falsified data but valid data.

Accordingly, the present invention improves the reliability of image file data by applying an electronic signature to the image file data to be stored when the image file data is stored in the memory card by the image forming apparatus. With the goal.

It is another object of the present invention to further improve the reliability by recording the electronic signature in a data storage area which can be set so as to prohibit writing by other than the image forming apparatus.

Another object of the present invention is to prevent tampering of image file data stored in a memory card and improve the reliability of the data.

[0008]

A memory card according to the present invention is a memory card having an area in which an electronic signature of image file data created by an image forming apparatus can be recorded. A data storage area that can be set to be prohibited is formed, and the electronic signature is recorded in the data storage area. According to another feature of the present invention, a secret key used for applying an electronic signature to image file data created by an image forming apparatus, and a public key paired with the secret key can be recorded. A memory card having an area, wherein a data storage area that can be set to prohibit writing by other than the image forming apparatus is formed, and the secret key and the public key are recorded in the data storage area. It is characterized by having.
Another feature of the present invention is that a private key unique to the device is held and an electronic signature is given using the private key unique to the device. Another feature of the present invention is that a secret key creating means for newly creating a secret key defined by a user is provided, and an electronic signature is performed using the secret key created by the secret key creating means. Features. Another feature of the present invention is that, in an image forming apparatus having an interface capable of accessing a memory card, a device-specific secret key or a user-defined secret key is stored in a property file area in the memory card. It is characterized by having a key storage unit that performs the key storage. Another feature of the present invention is that the apparatus further comprises key information display control means for visually displaying the device-specific secret key or a user-defined secret key on a display device. Another feature of the present invention is that the device has a device-specific public key that is paired with the device-specific secret key. Another feature of the present invention is that a public key creating means for creating a user-defined public key paired with the user-defined secret key is provided. Another feature of the present invention is that a data storage area that can be set to prohibit writing by a device other than a predetermined image forming apparatus is formed, and an electronic signature is recorded in the data storage area. An image forming apparatus provided with an interface that can access a memory card that has a key information storage unit that stores information on a device-specific public key or the user-defined public key in a property file in the memory card. It is characterized by. Another feature of the present invention is that the apparatus further comprises key information display control means for visually displaying a public key unique to the device or a public key defined by a user on a display device.
Another feature of the present invention is an image forming apparatus having data storage means for storing created image file data in a memory card, wherein a one-way function is used for the image file data. Calculating means for calculating a message digest value unique to the image file data; signing means for encrypting the message digest value with a device-specific secret key or a user-defined secret key to obtain a signature; Storage means for storing the image file data to be signed in the image file area of the memory card, in addition to the storage means for storing the image file data in the memory card in the property area.

The image forming method of the present invention is characterized in that a secret key creation process for newly creating a secret key defined by a user is performed, and an electronic signature is given using the secret key created in the secret key creation process. . Another feature of the present invention is an image forming method using an apparatus having an interface capable of accessing a memory card,
Key storage processing for storing a device-specific secret key or a user-defined secret key in a property file area in the memory card is performed. Another feature of the present invention is that a key information display control process of visually displaying a secret key unique to the device or a secret key defined by a user on a display device is performed. Another feature of the present invention is that an electronic signature is given using a device-specific public key that is paired with the device-specific secret key. Another feature of the present invention is that a public key creation process for creating a user-defined public key that is paired with the user-defined secret key is performed. Another feature of the present invention is that, in an image forming method using an apparatus having an interface capable of accessing a memory card, the device-specific public key or user-defined Is characterized in that key information storage processing for storing a public key is performed. Another feature of the present invention is that display control processing for visually displaying the device-specific public key or a user-defined public key on a display device is performed. Another feature of the present invention is an image forming method for performing a data saving process of saving created image file data in a memory card, using a one-way function for the image file data. A calculation process of calculating a message digest value unique to the image file data; a signature process of encrypting the message digest value with a device-specific secret key or a user-defined secret key to obtain a signature; And storing the image file data to be signed in the image file area of the memory card.

A storage medium according to the present invention is characterized in that a program constituting each means described above is stored so as to be readable from a computer. Another feature of the present invention is that a program for executing the above-described image forming method is stored in a computer-readable manner.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a memory card, an image forming apparatus, an image forming method and a storage medium according to the present invention will be described with reference to the drawings. "First Embodiment" Currently, RSA is used as a digital signature technology.
(Rivest-Shamir-Adelman) and other systems using a so-called asymmetric public key system. In the asymmetric public key method, a pair of key information of a “public key” and a “secret key” is set.

FIG. 13 and FIG. 14 conceptually explain the electronic signature. In this technology,
"Message digest value" and "public key" in FIG.
Is the point. The message digest value has a unique value for each message.

First, a message digest value is calculated for data (text or binary) to be signed. The message digest value is created from the data to be signed using a one-way function (hash function), and is a value unique to the data to be signed. Then, the message digest value created as described above is encrypted with the secret key.

When transmitting and receiving electronic data, the transmitting side sends the message digest value encrypted with the secret key as a signature to the receiving side together with the data to be signed. The receiving side decrypts the received signature data with the public key of the signature side to obtain a message digest value. And
The message digest value calculated from the received signature target data is compared with the decrypted message digest value. The signature can be verified by the above-described procedure. Hereinafter, the present embodiment will be described in more detail. FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus having a function of preventing image file data from being tampered according to the present embodiment. This image device is a control device (CP
U) 41, memory 42, input device 43, output device 44,
And a memory card I / F 45. The image forming apparatus may also include a network I / F 46 and an external recording device 47 depending on the situation.

The control unit 41 manages the operation of each unit of the image forming apparatus, and is composed of a microprocessor and its peripheral circuits. Memory 42
Are, for example, ROM (Read Only Memory), RAM (Ra
and a program executed by the image forming apparatus, data used for processing, data created by a user, and the like.

The input device 43 corresponds to, for example, a keyboard, a pointing device, a touch panel, and the like, and is used for instructing the control device 41 to perform various operations. The output device 44 corresponds to, for example, a CRT or a liquid crystal display device, and displays a message from the system, a visualized model diagram, and the like.

The memory card I / F 45 is a memory card 4
8 to read data stored in the memory 42,
Is written in the memory card 48.

The external recording device 47 is, for example, a magnetic disk device, an optical disk device, a magneto-optical disk device, or the like.
The above-described programs and data can be stored, and can be used by loading them into the memory 42 as needed.

The network I / F 46 communicates with an external device via an arbitrary network (line) such as a LAN and a modem. As a result, the program and the data can be received from an external device via a network as needed, and can be loaded into the memory 42 and used.

FIG. 2 is a diagram showing an example of a memory map of the memory card 48, in which image file data, a signature of the image file data, and a property file are stored. The property file is basically ASCII
The information is described in a text format using only codes, and when an image file is to be printed, the specification information is completed for each print job.

There is one property file in the memory card 48, and the target image file data can be stored in any location. Further, in the present embodiment, a normal area that can be drawn by any image forming apparatus,
By setting the access right, a data storage area that can be set so as to prohibit writing by a designated or formed image forming apparatus other than the image forming apparatus is set, and image file data or The signature of the image file data can be stored.

Next, an example of the control means provided in the image forming apparatus in order to prevent the falsification of the image file data according to the first embodiment having the above-described configuration will be described with reference to the apparatus configuration block shown in FIG. This will be described with reference to FIGS.

In this embodiment, as shown in FIG.
A message digest value of data to be signed is calculated using a hash function called D5. MD5 is currently one of the encryption programs PG
This is the message digest function actually used in P (Pretty Good Privacy).

When the user attempts to save the image file data created by the user in the memory card 48 in the image forming apparatus, the user instructs the saving process from the input device 43 and the signal is input to the control device 41. Thus, the control is started.

The control device 41 displays the intention on the output device 44 in order to confirm with the user whether or not the data is to be digitally signed (step S61). FIG. 5 is a diagram showing an example of this intention display, and the present invention is not limited to this. If the signature is not to be performed, the image file data is immediately stored in the normal area of the memory card 48, and the control process ends (step S66).

On the other hand, when performing the signature, a message digest value of the image file data to be signed is calculated (step S62), and the message digest value is encrypted with a device-specific secret key held by the image forming apparatus ( In step S63, the encrypted message digest value is stored as a signature in a non-writable area of the memory card 48 except for the target device (step S64).
It should be noted that the device-specific public key that is paired with the device-specific secret key is also held in the image forming apparatus.

Finally, the image file data to be signed is stored in a non-writable area other than the target device of the memory card 48 (step S65), and the control process ends.
The user may be allowed to select the signature or the storage area of the image file data to be signed.

According to the present embodiment, when storing image file data in a memory card, a message digest value of the image file data is calculated using a one-way function, and the message digest value is calculated using a secret key. Since the message digest value is signed and stored in the memory card together with the image file data, falsification of the image file data can be reliably prevented, and the reliability of the image file data is improved. be able to.

[Second Embodiment] In the first embodiment described above, the electronic signature method using a device-specific secret key and a device-specific public key has been described. In the embodiment, a method of performing an electronic signature using a secret key and a public key defined by a user will be described.

An example of a control procedure of an image forming apparatus provided with a method for preventing image file data tampering according to the second embodiment will be described with reference to the block diagram of the apparatus configuration in FIG. 1 and the flowchart in FIG. .

When saving the image file data created by the user in the memory card 48, the user instructs the saving process from the input device 43, and the control is started by being input to the signal control device 41. .

The control device 41 displays the intention on the output device 44 side in order to confirm with the user whether or not the data is to be digitally signed (step S71). When the signature is not performed, the image file data is immediately stored in the normal area of the memory card 48, and the control process ends.

On the other hand, when performing the signature, the control device 41 indicates to the user whether to use the device-specific secret key, to create a new user-defined secret key, or to indicate the intention on the output device 44 ( Step S72).

FIG. 7 is a diagram showing an example of this intention display, but the present invention is not limited to this. When creating a user-defined secret key, the control device 41 asks the user to input an arbitrary password (step S7).
3) Automatically create a user-defined secret key based on the input personal identification number (step S74).

Thereafter, a user public key is automatically generated from the secret key defined by the user (step S7).
5). Thereafter, a message digest value of the image file data to be signed is calculated (step S76), and the message digest value is encrypted with a secret key unique to the selected device or a user-defined secret key (step S76).
77) The encrypted message digest value is stored as a signature in a non-writable area of the memory card 48 except for the target device (step S78).

Finally, the painter file data to be signed is stored in a non-writable area of the memory card 48 other than the target device (step S79), and the control process is terminated.
Thus, a secret key unique to the device, a secret key other than the public key, and a public key can be used.

Further, according to the present embodiment, since a user-defined secret key is newly created and an electronic signature is applied, an electronic signature that is difficult to be tampered can be performed.

Further, according to the present embodiment, since the user can create a secret key used for signing, a secret key unique to the device, a secret key other than the public key, and a public key can be used. The reliability of the signed image file data can be further improved. In the above-described second embodiment, a method has been described in which an electronic signature is created using a secret key other than the device-specific secret key by newly creating a user-defined secret key. In the third embodiment, a secret key and a user public key defined by a user are stored in the image forming apparatus, and a method of using them will be described.

[Third Embodiment] An example of a control procedure of an image forming apparatus having a method for preventing falsification of image file data according to the third embodiment will be described with reference to FIG. This will be described with reference to the flowchart of FIG.

When saving the image file data created by the user in the memory card 48, the user instructs the saving process from the input device 43, and the control is started by being input to the signal control device 41. .

The control device 41 displays the intention on the output device 44 in order to confirm with the user whether or not the data is to be digitally signed (step S801). When the signature is not performed, the image file data is immediately stored in the normal area of the memory card 48, and the control process ends.

On the other hand, when performing the signature, the control device 41 asks the user whether to use a device-specific secret key or a user-defined secret key stored in the device.
A new user-defined secret key is created or its intention is displayed on the output device 44 (step S802). FIG.
Is a diagram showing an example of this intention display, but the present invention is not limited to this. When a user-defined secret key is not used, the first embodiment is followed.

When a new user-defined secret key is created, a secret key PIN is entered according to the second embodiment (step S803), and a secret key and a public key are created. The public key is stored in the external recording device 46 or the memory 42 (step S80).
4). However, the stored private key and public key can be deleted from the external recording device 46 or the memory 42 at the discretion of the user.

On the other hand, if the result of determination in step S 802 is that no new secret key is to be created, the flow advances to step S 813 to determine whether to use a registered secret key. As a result of this determination, when a user-defined secret key stored in the device is used, the personal identification number set for the secret key is input (step S806), and the secret key belongs to the user. Is verified (step S8).
07). Here, if there are a plurality of stored user-defined secret keys, the user is allowed to select one of them,
The selected secret key is verified. Then, if the user is authenticated, it is checked whether the public key paired with the secret key exists in the external storage device 46 or the memory 42 (step S808). Is created and stored in the external storage device 46 or the memory 42 (step S805).

In step S809, a message digest value of the image file data to be signed is calculated, the message digest value is encrypted with the secret key defined by the user (step S810), and the encrypted message digest value is signed. Is stored in the memory card 48 (step S811). Finally, the image file data to be signed is stored in the memory card 48 (step S812), and the control process ends.

[Fourth Embodiment] In the embodiments described above, only the image file data to be signed and the signature are stored in the memory card 48. In the fourth embodiment, a method of storing a public key and a private key for confirming a signature in a memory card 48, and an output device 44 of an image forming apparatus
Will be described.

An example of a control procedure of an image forming apparatus provided with a method for preventing image file data tampering according to the fourth embodiment will be described with reference to a block diagram of the apparatus configuration of FIG. 1 and a flowchart of FIG. .

The procedure for saving the signature target image file data and the signature created by the user in the memory card 48 is the same as in the previous embodiments. Thereafter, the control device 41
Displays the intention on the output device 44 in order to confirm with the user whether the secret key used for the image file and the public key corresponding thereto are stored in the memory card 48 or displayed on the display device (step S901). ). FIG. 11 shows an example of this intention display, but the present invention is not limited to this.

Next, items to be selected for the storage and display methods of the private key and the public key appear on the output device side (step S).
902), FIG. 12 is an example of this intention display, but the present invention is not limited to this. In particular, since the public key is used to verify the image file data and the signature,
It needs to be saved in some way. You have the following options for handling them.

(Regarding Public Key) (1) The public key is stored in the same memory card 48 as the memory card 48 in which the image file data and the signature are stored. (2) The public key is stored in a memory card different from the memory card 48 in which the image file data and the signature are stored. (3) Display the public key on the output device.

(Regarding Private Key) (1) The private key is stored in the same memory card as the memory card 48 in which the image file data and the signature are stored. (2) The secret key is stored in a memory card different from the memory card 48 in which the image file data and the signature are stored. (3) Display the secret key on the output device.

In response to the questions in steps S903 and S909, after selecting the method of storing and displaying the secret key and the public key, the secret key and the public key are stored in a memory storing signed image file data. Is stored in the same memory card as the card 48 (steps S904 and S9).
10).

When the secret key and the public key are stored in a memory card different from the signed image file data in response to the question in step S915, the user is instructed to exchange the memory card 48 and then exchanged. After recognizing the memory card 48, the secret key and the public key are stored (steps S916 and S917).

In response to the question in step S905,
If the private key is to be stored in a memory card separate from the data, the private key storage flag is turned on in step S906.
To If the public key is to be stored in a memory card separate from the data in response to the question in step S911, the public key storage flag is turned on in step S912.

When the secret key and the public key are displayed on the output device 44 in response to the questions in steps S907 and S913, the secret key and the public key are displayed on the output device (steps S908 and S914). After storing and displaying the secret key and the public key, the control device 41 ends the process. These secret keys and public keys can be stored in a non-writable area of the memory card 48 other than the image forming apparatus by a user's selection.

Further, according to the present embodiment, the secret key and the public key created by the user are stored in the image forming apparatus, so that the secret key and the public key can be more easily used when reusing the same. Can do it.

Further, according to the present embodiment, the secret key used for the signature and the public key corresponding to the secret key are stored in the memory card, and the secret key and the public key are displayed on the output device of the image forming apparatus. Thus, the user can store the secret key and the public key, can easily use the public key at the time of verification, and can reuse the secret key.

(Other Embodiments of the Present Invention) The present invention can be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.) and can be applied to an apparatus composed of one device. May be applied.

Further, the functions of the above-described embodiment are implemented in an apparatus connected to the above-described various devices or a computer in a system so that various devices are operated so as to realize the functions of the above-described embodiment. Software to do. And the computer (CPU or MP) of the system or apparatus.
The invention implemented by operating the various devices according to the program stored in U) is also included in the scope of the present invention.

In this case, the above software is used. The program code itself realizes the functions of the above-described embodiment, the program code itself, and a means for supplying the program code to a computer,
For example, a storage medium storing such a program code constitutes the present invention. As a storage medium for storing such a program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, C
D-ROM, magnetic tape, nonvolatile memory card, R
OM or the like can be used.

When the computer executes the supplied program code, not only the functions described in the above-described embodiments are realized, but also the OS (operating system) or the operating system running on the computer. It goes without saying that such a program code is included in the embodiment of the present invention even when the functions described in the above-described embodiment are realized in cooperation with other application software or the like.

Further, after the supplied program code is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, the function expansion board or the function expansion unit is specified based on the instruction of the program code. The present invention also includes a case where a CPU or the like provided in the apparatus performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

According to each of the above embodiments, a signature, image file data, a secret key, and a public key can be stored in a non-writable area of the memory card other than the image forming apparatus by a user's selection. File security can be improved.

[0064]

As described above, according to the present invention,
It is possible to effectively prevent tampering of image file data created by the image forming apparatus and stored in the memory card, and it is possible to greatly improve the reliability of the image file data.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an image forming apparatus having a function of preventing image file data from being tampered.

FIG. 2 is an explanatory diagram showing an example of a memory map of a memory card.

FIG. 3 is a flowchart illustrating a processing procedure of the image forming apparatus according to the first embodiment.

FIG. 4 is a diagram illustrating the relationship between electronic data and a message digest value.

FIG. 5 is an explanatory diagram illustrating an example of a display unit of the image forming apparatus according to the first embodiment.

FIG. 6 is a flowchart illustrating a processing procedure of the image forming apparatus according to the second embodiment.

FIG. 7 is an explanatory diagram illustrating an example of a display unit of an image forming apparatus according to a second embodiment.

FIG. 8 is a flowchart illustrating a processing procedure of the image forming apparatus according to the third embodiment.

FIG. 9 is an explanatory diagram illustrating an example of a display unit of an image forming apparatus according to a third embodiment.

FIG. 10 is a flowchart illustrating a fourth embodiment.

FIG. 11 is an explanatory diagram illustrating an example of a display unit of an image forming apparatus according to a fourth embodiment.

FIG. 12 is a diagram illustrating an example of a display unit of an image forming apparatus according to a fourth embodiment.

FIG. 13 is an explanatory diagram related to an electronic signature.

FIG. 14 is an explanatory diagram related to an electronic signature.

[Explanation of symbols]

 Reference Signs List 41 control device 42 memory 43 input device 44 output device 45 memory card I / F 46 network I / F 47 external storage device 48 memory card

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H04L 9/32 H04L 9/00 675B

Claims (21)

[Claims] 1. A memory card having an area in which an electronic signature of image file data created by an image forming apparatus can be recorded, wherein a data storage area that can be set to prohibit writing by other than the image forming apparatus is provided. A memory card formed, wherein the digital signature is recorded in the data storage area. 2. A memory card having an area in which a secret key used for applying an electronic signature to image file data created by an image forming apparatus and a public key paired with the secret key can be recorded. A memory card, wherein a data storage area that can be set to prohibit writing by other than the image forming apparatus is formed, and the secret key and the public key are recorded in the data storage area. . 3. An image forming apparatus, wherein a private key unique to a device is held, and an electronic signature is given using the private key unique to the device. 4. An image forming apparatus comprising: a secret key creating unit for newly creating a secret key defined by a user; and performing an electronic signature using the secret key created by the secret key creating unit. 5. An image forming apparatus having an interface capable of accessing a memory card, comprising: a key storage unit for storing a device-specific secret key or a user-defined secret key in a property file area in the memory card. Characteristic image forming apparatus. 6. The image forming apparatus according to claim 5, further comprising key information display control means for visually displaying the device-specific secret key or a user-defined secret key on a display device. 7. The image forming apparatus according to claim 5, further comprising a device-specific public key that is paired with the device-specific secret key. 8. The image forming apparatus according to claim 5, further comprising a public key creating unit that creates a user-defined public key that is paired with the user-defined secret key. . 9. A data storage area which can be set so as to prohibit writing by a device other than a predetermined image forming apparatus, and which can access a memory card in which an electronic signature is recorded in the data storage area. An image forming apparatus provided with an interface, further comprising a key information storage unit configured to store information on a device-specific public key or a user-defined public key in a property file in the memory card. 10. The image forming apparatus according to claim 9, further comprising key information display control means for visually displaying the device-specific public key or a user-defined public key on a display device. 11. An image forming apparatus having data storage means for storing created image file data in a memory card, wherein a message unique to the image file data is obtained by using a one-way function for the image file data. Calculating means for calculating a digest value; signing means for encrypting the message digest value with a secret key unique to the device or a secret key defined by a user to obtain a signature; and storing the signature in a property area in a memory card. And a storage unit for storing the image file data to be signed in the image file area in the memory card. 12. An image forming method comprising: performing a secret key creation process for newly creating a secret key defined by a user; and performing an electronic signature using the secret key created by the secret key creation process. 13. An image forming method using an apparatus having an interface capable of accessing a memory card, wherein a key storage process for storing a device-specific secret key or a user-defined secret key in a property file area in the memory card. Image forming method. 14. The image forming method according to claim 13, wherein a key information display control process of visually displaying the device-specific secret key or a user-defined secret key on a display device is performed. 15. The image forming method according to claim 13, wherein an electronic signature is given using a device-specific public key that is paired with the device-specific secret key. 16. The image forming method according to claim 13, wherein a public key creation process for creating a user-defined public key paired with the user-defined secret key is performed. . 17. An image forming method using an apparatus having an interface capable of accessing a memory card, wherein key information storage for storing a device-specific public key or a user-defined public key in a property file in the memory card. An image forming method comprising performing a process. 18. The image forming method according to claim 17, wherein a display control process of visually displaying the device-specific public key or a user-defined public key on a display device is performed. 19. An image forming method for performing a data saving process of saving created image file data in a memory card, wherein a message unique to the image file data is obtained by using a one-way function for the image file data. Calculating a digest value, encrypting the message digest value with a device-specific secret key or a user-defined secret key to obtain a signature, and storing the signature in a property area in a memory card. And storing the image file data to be signed in an image file area in the memory card. 20. A storage medium storing a program constituting each means according to claim 1 so as to be readable from a computer. 21. A storage medium storing a program for executing the image forming method according to claim 12 so as to be readable from a computer.