JP2000298974A - An information recording method that makes media-specific information movable - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an information recording method for enabling transfer of media-specific information which enables information specific to a storage medium to be transferred to another storage medium while preventing unauthorized use. Is to do. SOLUTION: From storage medium A1 to storage medium B1
When the content A141 is moved to the storage medium A1,
Content ID / A1421 read out to management table
Is recorded, and the content data A1422 is
2. The content is recorded on the storage medium B1 as the content B142 via the unique unit 54 and the content recording unit 55, and the content A142 is deleted from the storage medium A1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes information unique to a storage medium having a media ID which is a unique identifier for each medium, reads out the information which has been made unique from the storage medium, and further stores other information. The present invention relates to an information recording method for moving media-specific information that can be appropriately moved to a medium and that can prevent unauthorized use of information.

[0002]

2. Description of the Related Art First, the terms information specificization and generalization will be described. Hereinafter, encrypting the data D with the encryption key K is expressed as E (K, D).

A method often used to prevent unauthorized use is to use a secret key that is shared between devices that record and use information and that is kept secret to users.
This secret key is called a device key R.

Further, by making information unique to a medium, even if the information is copied to another medium, the information cannot be properly decrypted on another medium, so that unauthorized use can be prevented. One example is a method using a unique identifier for each medium. A method using a unique identifier for each medium will be briefly described below.

[0005] An identifier (media ID) unique to each medium is written in advance in each medium in a rewritable manner. Therefore, when there are two media,
The media IDs of the two media do not match. When recording the purpose information C for preventing unauthorized use on such a medium, first, the medium ID (MI) is encrypted with the device key R, and E (R, M
Obtain I). Encrypted target information E (E (R, MI), C) generated by encrypting target information C using this as an encryption key
The media writes.

On the other hand, when reading the target information C,
The recorded encryption purpose information E (E (R, MI),
C) and media ID (MI), MI is encrypted with the device key R to obtain E (R, MI), and E (E (R, MI), C) is decrypted using this as a decryption key. Purpose information C
Can be obtained.

At this time, it is considered that the encryption target information recorded on a certain medium A is copied to another medium B, and the encryption target information is read from the medium B.
At this time, the media ID (MIA) of the media A and the media ID (MIB) of the media B are different. Therefore, even if the encryption purpose information copied to the medium B is read as described above, the key (E (R, MI
A)) and the key (E (R, MIB)) used for decryption are different, so that the target information cannot be read accurately. That is, the encryption purpose information is valid only when recorded on the medium A, and invalid when recorded on another medium. This is called uniqueization of the target information to the media. By making the information unique to the medium, it becomes impossible to use the information even if it is copied to another medium, thereby preventing unauthorized use.

Further, the encryption purpose information E (E (R, M
To generate I) and C), it is necessary to know the device key R in addition to the media ID (MI) and the target information C. Conversely, in order to decrypt the encryption purpose information E (E (R, MI), C), it is necessary to know the device key R in addition to the media ID (MI). Therefore, if the device key R is kept secret, it is impossible to illegally generate encryption target information or generate target information from the encryption target information just because the media ID is known.

[0009] As described above, making information unique to a medium is a powerful method for preventing unauthorized use. Stated another way, since the information in the media is unique to the media, even if the information in the media is copied, it does not pose a threat to any unauthorized use prevention method. This is because the specialized information is properly decoded and meaningful only when recorded on the medium, and is completely meaningless when recorded on other media. .
That is, in order to use information unique to a medium, the medium must be physically owned. The right to use information is tied to physical media possession.

Therefore, the generation of the unique purpose information E (E (R, MI), C) from the media ID (MI) and the purpose information C is expressed as the purpose information being made unique by the media ID. Generating the purpose information from the information and the media ID is expressed as generalizing the specific purpose information by the media ID.

As is apparent from the above description, there is no problem in preventing unauthorized use even if the unique information in the medium is copied to another medium. Therefore, the user can record the unique information in the medium as a backup on another medium such as a hard disk or MO. When a large amount of information has accumulated in the storage medium and the remaining storage capacity has been reduced, the user may copy some of the information to another storage medium as a backup and store the information in the storage medium. Is deleted, the remaining storage capacity can be increased. If necessary, the information can be copied from the backup to the storage medium and returned. The returned information can be used as valid information. It is very convenient for the user that the user can legally back up any number of information.

By the way, according to such a conventional method, information recorded on a storage medium for use cannot be moved for use on another storage medium. Is inconvenient.
This does not refer to backup, but to the fact that copying information to another medium and allowing the information to be used on that other medium creates room for unauthorized use. .

The transfer of information means, for example, transferring information from the medium A to the medium B. It is convenient for the user to be able to combine different pieces of information in two media into one medium, and at this time, it is necessary to move the information. What is important from the viewpoint of preventing unauthorized use of information transfer is, for example, that information in the medium A cannot be used later when information is transferred from the medium A to the medium B. In other words, the transfer of information is the work of re-specificating the information unique to the medium A to the medium B. The right to use the information linked to the medium A before the movement is transferred to the medium B to transfer the information. It can be said that it is the work of linking.

In order to move between media, the following methods can be easily considered. First, the specialized information in the medium A is generalized. The generalized information is made unique to the medium B and recorded on the medium B. Then, the unique information in the medium A is deleted. If such a function is provided to the user, the transfer of the unique information between media can be realized for the time being.

However, the problem here is whether information in the media A, whose use is not permitted, cannot be used reliably. For example, consider a case where the information in the medium A has been backed up before the user performs the moving operation. After the moving operation is completed, the information in the medium A is erased as described above, so that the moved information does not remain in the medium A.
However, if a backup has been made in advance, this information is valid and can be used if this backup is copied back to the medium A and returned.

Although such illegal use can be prevented by prohibiting the backup, it is difficult to develop a technology for preventing the backup, particularly in the case of a simple storage medium that simply records. . Furthermore, above all, backup is a convenient function in itself, and prohibiting it is very inconvenient for users.

As described above, according to the conventional technology, when a function of moving information in a medium to another medium is provided to a user, the user can easily copy the information illegally and use it. Would.

[0018]

As described above, when it is attempted to move information unique to a medium to another medium, it is easy to copy a backup to the medium after the information is moved. There is a problem that unauthorized use is performed.

Preventing backup prevents unauthorized use, but preventing backup has a problem in that user convenience is impaired.

The present invention has been made in view of the above,
The purpose is to move the information unique to the storage medium to a different storage medium, and to transfer the media-specific information that can prevent improper use of the information by unauthorized copying while enabling backup. It is an object of the present invention to provide an information recording method which makes it possible.

[0021]

In order to achieve the above object, according to the present invention, a WAO area which can be written only once and a RAM area which can be rewritten many times can be used. Non-rewritable media I which has a unique identifier for each media
An information recording method for recording information on a storage medium in which D is written, wherein when recording target information on the storage medium, a search is made for a content ID available in the storage medium, And the content ID are combined to generate a media content ID, the target information is unique with the media content ID to generate content data, and the content ID is generated.
And recording the content obtained by combining the content data with the content data in the RAM area of the storage medium.

According to the first aspect of the present invention, a media ID is generated by combining a media ID and a content ID, and content data is generated by making target information unique by the media content ID. In order to record the content of the set of content data on the storage medium, the target information can be unique as a result of encrypting the media ID with the content ID, and another content key is prepared in advance, and the content is encrypted with the content key. It is also possible to reduce the content encryption processing by making the content key unique as the target information.

Further, the present invention described in claim 2 is the same as the claim 1.
In the invention described in the above, an invalid content ID management table for managing a content ID which cannot be used in the storage medium in the future is recorded in the WAO area, and the content recorded in the storage medium is read out. When acquiring the object information from the content, the content ID of the content read from the storage medium is the invalid content I
Check if it is recorded in the D management table,
If it is recorded, the acquisition process of the purpose information is stopped, and if the content ID of the content is not recorded in the invalid content ID management table, the media ID and the content ID are combined, The gist is to generate a media content ID, generalize the content data of the content with the generated media content ID, and acquire the target information.

According to the second aspect of the present invention, when the content ID of the content is recorded in the invalid content ID management table, the acquisition process of the target information is stopped. , The media ID and the content ID are combined to generate a media content ID, and the content data of the content is generalized with the media content ID to obtain the target information. It is not possible to acquire the purpose information of the content that has been set, and it is possible to generalize the content data as a result of encrypting the media ID with the content ID. Note that, although the content ID included in the content is not encrypted, and the content ID is illegally set to another value, the content may be changed to a content having a content ID different from the original content ID. As the content data included in the content, data unique with a value including the content ID is recorded, and the content data depends on the content ID. In this case, as described above, when reading the content data, the content data is generalized with a value including an ID that is not the original content ID, so that the information obtained as a result of the reading is not true honest information but meaningless information. Becomes Therefore, even if the content ID is changed from the original one, the information obtained only becomes meaningless.

Further, the present invention according to claim 3 provides the invention according to claim 1.
In the invention described in the above, an invalid content ID management table for managing a content ID that cannot be used in the storage medium in the future is recorded in the WAO area, and a content I that can be used in the storage medium is stored.
An available content ID management table for managing D is recorded in the RAM area, and when moving the content from the first storage medium to the second storage medium, the content is transferred from the first storage medium to the second storage medium. The content is read, and after confirming that the content ID of the read content is not recorded in the invalid content ID management table of the first storage medium, the content ID is recorded in the invalid content ID management table. And deletes the content ID from the available content ID management table of the first storage medium, and deletes the first media ID of the first storage medium.
And the content ID of the read content to generate a first media content ID.
Generalizing the content data of the content with the media content ID, obtaining the target information, combining the second media ID of the second storage medium with the content ID, and forming the second media content ID The content information is generated by generating the content information by making the target information acquired from the first storage medium unique with the second media content ID, and the content obtained by combining the content ID and the content data is stored in the second storage medium. The gist is that the content is recorded in the RAM area of the medium and the content recorded in the RAM area of the first storage medium is erased.

According to the third aspect of the present invention, when the content is moved from the first storage medium to the second storage medium, the content ID of the content read from the first storage medium is the first. Is not recorded in the invalid content ID management table of the first storage medium, and the first media ID and the content ID of the first storage medium are combined to form the first media content ID.
Is generated, the content data of the content is generalized with the first media content ID, the target information is acquired, and the second medium I of the second storage medium is obtained.
D and the content ID to generate a second media content ID, the target information acquired from the first storage medium is unique by the second media content ID to generate content data, and the content ID and the content data are generated. Is recorded in the second storage medium, the target information of the content recorded in the invalid content ID management table cannot be obtained. Therefore, the content of the first storage medium is backed up before moving. If the content has been moved, the content ID of the content is invalidated when the content is moved,
However, even if the content is copied to a storage medium and read and used as described above, the content cannot be read. In this case, the backup itself is not prohibited. In other words, if the backup is copied and returned to the storage medium after the content is moved while allowing the backup, the content cannot be used.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a system configuration for implementing an information recording method for enabling movement of media-specific information according to the first embodiment of the present invention. The system shown in FIG. 1 includes a storage medium 1 and an information recording device 2 for recording target information 3 while preventing unauthorized use of the storage medium 1.

The storage medium 1 is an identifier unique to each storage medium, and is a non-rewritable medium ID 1
1. WAO (Wr
ite AtOnce) area 13 and a RAM (Read Only Memory) area 14 which is a storage area that can be rewritten any number of times
Having. The WAO area 13 has an invalid content ID management table 131.

Here, the properties of the WAO area 13 will be described. Information can be written into the WAO area 13 only once. Once written, the information cannot be recovered. The minimum unit of the information to be written is a bit, and information can be written in a unit of one bit.

This will be described with an example. Consider an 8-bit WAO area. Initially, they are all "0" and all bits are writable.

"00000000" Next, the fourth bit is set to "1". This is possible.

"00010000" The fourth bit "1" cannot be changed to "0" in any manner thereafter.
This is a property of the WAO area.

Still another bit can be a "1". For example, if the seventh bit is set to “1”, “00010
010 ". When writing is performed in this manner, the state of all "1" s and "11111111"
become. From this state, the state cannot be changed by any operation thereafter.

The RAM area 14 stores available contents I
It has a D management table 141 and a plurality of contents 142. The available content ID management table 141 indicates that when the content is backed up to another while the right to use the content is retained and the content is erased from the storage medium 1, the content to be newly recorded on the storage medium 1 after that is deleted. On the other hand, it is used to prevent the content ID of the content that has been backed up and deleted from being used. The content 142 has a content ID 1421 and content data 1422.

The information recording apparatus 2 receives two elements, a media ID 11 from the storage medium 1 and an available content ID 1421 from the available content ID management table 141, and outputs a result obtained by combining the two inputs. ID creating means 21 and unique means 22 for making the target information 3 unique with the media content ID output from the media content ID creating means 21
, Content ID 1421 and content data 142
2 has a content recording unit 23 for recording the content 142 made up of 2 in the RAM area 14. Also, the unique unit 22 has a device key 221.

FIG. 2 shows the format of the invalid content ID management table 131. This is a simple bit string, and each bit indicates whether or not the corresponding content ID is invalid. The correspondence between the bits in the table 131 and the content ID is such that the offset distance from the head of the bit string matches the number of the content ID. The initial value of the bit value is 0, and the corresponding bit is set to 1 when the content ID becomes invalid. The invalid content ID management table 131 shown in FIG. 2 indicates that the content IDs 8 and 13 are invalid.
The size of the invalid content ID management table 131 is set to 16
Assuming that it is KB, 16 × 1024 × 8 = 13107
Two content IDs can be managed. The initial values of the invalid content ID management table 131 at the time of shipment of the storage medium 1 are all 0. Since the invalid content ID management table 131 is recorded on the WAO area 13, a bit once set to 1 cannot be set to 0 again. Therefore, any content ID cannot be deleted from the invalid content ID management table 131.

Available content ID management table 14
1 is invalid content ID management table 1
31 and the size of the table is the same. Available content ID at the time of shipping storage medium 1
The initial values of the management table 141 are all 1.

In the following processing, recording a content ID in the content ID management table means that a bit in the table corresponding to the content ID is set to 1. Deleting a content ID from the content ID management table means setting a bit in the table corresponding to the content ID to 0.

In the first embodiment configured as described above, when the target information C3 is recorded on the storage medium 1, first, the media ID (MI) 11 is read from the storage medium 1 by the media content ID creating means 21. , A content ID (C) obtained by searching for an available content ID from the available content ID management table 141.
From the two inputs of I), the media content ID (MC
Generate I). MCI = MI + CI. At this time, the content ID (CI) is deleted from the available content ID management table 141.

Next, the unique unit 22 uniques the target information C with the media content ID to generate unique information. Assuming that the device key 221 is R, this unique information is E
(E (R, MCI), C). Finally, the CI is assigned to the content ID 1421, and the unique information E (E (R, M
The content 142 with CI) and C) as content data 1422 is recorded in the RAM area 14 of the storage medium 1 by the content recording means 23.

FIG. 3 is a block diagram showing a system configuration for implementing the information recording method according to the second embodiment of the present invention. The system shown in FIG. 3 includes a storage medium 1, an information use device 4 that reads information from the storage medium 1, and target information 3. The configuration of the storage medium 1 is the same as that of FIG.

The information use device 4 reads the content 142 from the storage medium 1, and furthermore, sets the content ID 1421 of the read content 142 to the invalid content ID.
A content reading unit 41 for checking whether or not the content is included in the management table 131;
D creating means 43 and media content ID creating means 4
3 has a generalization means 42 for generalizing the content data 142 with the media content ID output from the third. The generalization unit 42 has a device key 421. The device key 421 in the generalization unit 42 is the same as the device key 221 in the above-described unique unit 22.

A case where the content 142 is read from the storage medium 1 will be described. In this description, the storage medium 1 and the content 142 written in the first embodiment are used. That is, the content ID 1421 is CI, and the content data 1422 is E (E (R, MCI), C).
And the media ID 11 is MI. First, the content 142 is read by the content reading means 41, and the content ID (CI) and the content data E (E (R, MCI), C) are read. Further, the content reading means 41 reads the read content ID.
It is checked whether (CI) is not included in the invalid content ID management table 131. If it is included, the operation ends immediately. If not included, the operation is continued, and the content ID (CI) and the media ID 11 (M
I) to media content ID (MI + CI = MC)
I), and further generalizes the content data E (E (R, MCI), C) with the media content ID (MCI) using the generalization means 42 to obtain the target information C.

FIG. 4 is a block diagram showing a system configuration for implementing the information recording method according to the third embodiment of the present invention. The system shown in FIG. 4 includes a storage medium A1, a storage medium B1, and an information transfer device 5 that transfers information from the storage medium A1 to the storage medium B1. The configurations of the storage media A1 and B1 are the same as those shown in FIGS.

The information transfer device 5 includes a content reading unit 51, a generalizing unit 52, a media content ID creating unit 53, a unique unit 54, and a content recording unit 55. The device key 521 in the generalization unit 52 is the same as the device key 541 in the unique unit 54.

The case of moving contents from the storage medium A1 to the storage medium B1 will be described. Content reading means 51, media content ID creating means 53,
The operation of the generalization means 52 is the same as that of the second embodiment except for some exceptions. The exception is that the content reading means 51 reads out the content ID / A142
1 is deleted from the available content ID management table A141 (corresponding bit is changed from 1 to 0), and the content ID / A1421 is similarly recorded in the invalid content ID management table A131 (corresponding bit is changed from 0 to 1). That the content A142 is in the RAM area A14
Is to be removed from. In this way, the generalizing means 52 generates generalized information and passes it to the specificizing means 54.
Hereinafter, the operations of the unique unit 54, the media content ID creation unit 53, and the content storage unit 55 are the same as those in the first embodiment. Thus, the content B142 is recorded on the storage medium B1.

FIG. 5 is a block diagram showing a system configuration for implementing the information recording method according to the fourth embodiment of the present invention. The system shown in FIG. 5 includes a storage medium 1, a backup device 6, and a magnetic disk 7. The backup device 6 has a content reading unit 61 and a content recording unit 62. Although the configuration of the storage medium 1 is partially omitted, it is the same as that shown in FIGS. 1, 3, and 4.

When the content is backed up from the storage medium 1 to the magnetic disk 7, the content reading means 61 reads the content 142 and records it on the magnetic disk 7. When copying and restoring (restoring) the data backed up from the magnetic disk 7 to the storage medium 1, the content recording unit 62 reads the data from the magnetic disk 7 and records the data as the content 142 in the RAM area 14.

FIG. 6 is a block diagram showing a system configuration for implementing the information recording method according to the fifth embodiment of the present invention. The system shown in FIG. 6 includes a storage medium 1 and a deletion device 8. The deleting device 8 is a content deleting unit 81
Having. Although the configuration of the storage medium 1 is partially omitted, it is the same as that shown in FIGS. 1, 3, and 4.

To delete the content 142 from the storage medium 1, the content deleting means 81
D1421, the content ID is deleted from the available content ID management table 141, and the content 142 is deleted from the storage medium 1.

Here, the unauthorized user backs up the contents C of the storage medium A to the magnetic disk, moves the contents C from the storage medium A to another storage medium B, and then restores the data of the magnetic disk to the storage medium A. In this case, the content I of the restored content
D is recorded in the invalid content ID management table of the medium A. Therefore, the restored content cannot be read using the information using apparatus described in the second embodiment. In other words, unauthorized use by backup is prevented.

[0052]

As described above, according to the present invention,
The media ID and the content ID are combined to generate a media content ID, and the target information is stored in the media content I.
D to generate content data and record the content in which the content ID and the content data are combined into a storage medium.
The purpose information can be made unique by the result of encryption in
It is also possible to reduce the content encryption process by preparing another content key in advance, encrypting the content with the content key, and making the content key unique as the target information.

Further, according to the present invention, when the content ID is recorded in the invalid content ID management table, the acquisition process of the target information is stopped, and when not recorded, the media ID and the content ID are not recorded. To generate a media content ID, generalize the content data of the content with the media content ID,
Since the target information is obtained, the target information of the content recorded in the invalid content ID management table cannot be obtained, and the content data can be generalized as a result of encrypting the media ID with the content ID.

Further, according to the present invention, when the content is moved from the first storage medium to the second storage medium, it is confirmed that the content ID is not recorded in the invalid content ID management table. Generating a first media content ID by combining the first media ID and the content ID of the first storage medium, generalizing the content data of the content with the first media content ID, acquiring the target information, A second media content ID is generated by combining the second media ID and the content ID of the second storage medium, and the target information acquired from the first storage medium is converted to the second media content ID.
To generate the content data by
Since the content in which the D and the content data are combined is recorded in the second storage medium, the purpose information of the content recorded in the invalid content ID management table cannot be obtained. If the content has been backed up, the content ID of the content is invalidated when the content is moved. Therefore, after the movement, the backup is copied to the first storage medium, and the content is read and used as described above. It cannot be read. That is, the user can make a backup, but even if the backup is made, illegal use of information can be properly prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a system configuration for implementing an information recording method for making media-unique information movable according to a first embodiment of the present invention.

FIG. 2 shows an invalid content I used in the embodiment of FIG.
It is a figure showing the format of a D management table.

FIG. 3 is a block diagram showing a system configuration for implementing an information recording method for making media-unique information movable according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a system configuration for implementing an information recording method for making media-unique information movable according to a third embodiment of the present invention.

FIG. 5 is a block diagram showing a system configuration for implementing an information recording method for enabling movement of media-specific information according to a fourth embodiment of the present invention.

FIG. 6 is a block diagram showing a system configuration for implementing an information recording method for enabling movement of media-specific information according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage medium 2 Information recording device 3 Objective information 4 Information utilization means 5 Information transfer means 6 Backup device 8 Deletion device 11 Media ID 13 WAO area 14 RAM area 21 Media content ID creation means 22 Uniqueness means 23 Content recording means 42, 52 Generalization means 131 Invalid content ID management table 141 Available content ID management table 142 Content 1421 Content ID 1422 Content data

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B017 AA06 BA05 BA07 CA06 CA11 CA16 5D110 AA16 AA17 DA02 DA11 DB03 DC28 DD13 DD16 DE04

Claims (3)

[Claims] 1. A medium having a WAO area which is a storage area which can be written only once and a RAM area which is a storage area which can be rewritten many times, and a non-rewritable medium ID which is a unique identifier for each medium is written. An information recording method for recording information in a storage medium, wherein when recording target information in the storage medium, a search is made for a content ID available in the storage medium, and the media ID and the content ID are searched for. To generate a media content ID, generate the content data by uniquely identifying the target information with the media content ID, and store the content obtained by combining the content ID and the content data with the RAM area of the storage medium. Media-specific information, which is recorded in the media, can be moved Information recording method. 2. An invalid content I for managing a content ID which cannot be used in the storage medium in the future.
When the D management table is recorded in the WAO area, the content recorded in the storage medium is read, and when the target information is obtained from the read content, the content of the content read from the storage medium is read. Check whether the ID is recorded in the invalid content ID management table, and if it is recorded, stop the acquisition process of the target information, and record the content ID of the content in the invalid content ID management table If not, combining the media ID and the content ID to generate a media content ID, generalizing the content data of the content with the generated media content ID, and obtaining the target information 2. The media specific according to claim 1, wherein: Information recording method that makes coded information movable. 3. An invalid content I for managing a content ID which cannot be used in the storage medium in the future.
D management table is recorded in the WAO area, and an available content ID management table for managing a content ID available in the storage medium is recorded in the RAM area. When the content is moved to the storage medium, the content is read from the first storage medium, and the content ID of the read content is the first
After confirming that the invalid content ID is not recorded in the invalid content ID management table of the storage medium, the content ID is recorded in the invalid content ID management table, and the content ID is recorded in the use of the first storage medium. Delete from the possible content ID management table, combine the first media ID of the first storage medium with the content ID of the read content, and
The content data of the content is generalized with the first media content ID, the target information is obtained, and the second media ID of the second storage medium and the content ID are obtained. Combine to form the second media content I
D, generating the target data acquired from the first storage medium with the second media content ID to generate content data, and converting the content obtained by combining the content ID and the content data into the second content. 2. The information for making the media unique information movable according to claim 1, wherein the content is recorded in the RAM area of the storage medium, and the content recorded in the RAM area of the first storage medium is deleted. Recording method.