JP2005175652A - Content distribution system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a content distribution system for safely and efficiently distributing contents even when an intermediate are employed for the distribution. <P>SOLUTION: An author apparatus embeds a hash value of a signature of metadata including a public key certificate of a distribution destination and right permission information to contents as an electronic watermark and thereafter distributes the resulting contents to an intermediate apparatus. The intermediate apparatus signs the metadata including the public key certificate of the distribution destination and the right permission information and distributes the resulting metadata to a viewer apparatus. The viewer apparatus verifies the signature, the metadata and the electronic watermark and thereafter reproduces / utilizes the contents. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a copyright protection system for digital content, and more particularly, to a copyright protection technology for adding metadata to content and embedding information related to the metadata with a digital watermark and distributing it safely.

  In recent years, contents such as images and music have been digitized and distributed via storage media or communication media. In order to protect the copyright of such digitized content information, copyright information, rights information, etc. can be reliably added to the content as metadata, and the content can be distributed according to the content of the metadata. It is essential.

  As a conventional copyright protection technique, there is a technique for embedding an electronic signature or hash value of metadata such as copy control information in a content with a digital watermark to prevent unauthorized use of the content (for example, see Patent Document 1). Specifically, information such as copy control information, transmission source ID, and transmission destination ID of the target content is added as metadata, and an electronic signature is applied if necessary to prevent falsification of the metadata. Embed signature or metadata hash value with digital watermark. When using content, if the signature of the metadata is added, the signature can be verified to detect tampering of the metadata, and the digital watermark detected from the content and the signature or signature can be detected. By comparing the hashes, it is possible to verify the validity of the metadata and the content. From the characteristics of the digital watermark, it is possible to verify the validity even when the content is converted by media conversion such as compression.

  In addition, as a conventional electronic signature technology, by adding the electronic signature to the message data plus the participant's identifier, the data is circulated to prevent the alteration of the circulation route information and add information during the circulation. There is a technology that makes it possible (see, for example, Patent Document 2).

JP 2003-122726 A

JP-A-7-162451

  In a conventional content distribution system using a copyright protection technique such as Patent Document 1, when transmitting metadata composed of additional information such as content copyright information and rights information together with the content, the author device Used digital signatures to prevent metadata tampering.

  The viewer device verifies that the received metadata has not been tampered with by verifying the signature, compares the detected digital watermark information with the signature or hash value, confirms the validity, and then rights information, etc. The content was used according to Here, the use of content depends on the form of the content. For example, when the content is a still image, display, printing, etc., when it is a moving image, viewing, recording, etc., and when it is audio, playback, recording, etc. mean use of the content.

  However, in the conventional configuration, when the content is distributed through the mediator device, it has been impossible for the mediator device to add restrictions on new rights information. Alternatively, if an unspecified intermediary device is configured so that the right information can be added or updated, the content can be illegally used.

  In addition, when content is distributed directly to each viewer device without intermediary devices, the signature of the metadata is different, so it is necessary to re-embed the digital watermark for each distribution. In general, embedding a digital watermark into video content or the like is heavy in processing and takes time, so re-embedding the digital watermark for each viewer device is a problem in actual operation.

  Also, the bit length of an electronic signature, which is generally said to be secure, is currently 1024 bits for RSA and 160 bits for elliptic curve cryptography, and is expected to become even longer in the future. However, in general, the number of bits that can be embedded in video content with a digital watermark is about 64 to 100 bits. For this reason, it is difficult to embed the signature itself with a digital watermark.

  The present invention solves the above problems and provides a copyright protection technique that allows content to be distributed safely and efficiently even when an intermediary device is sandwiched between the author device and the viewer device.

  In the content distribution system of the present invention, the author device creates metadata of the created or retained content, applies an electronic signature to the created metadata using the author's private key, and hashes the signature A value (for example, 64 bits) is embedded as digital watermark information in the content, and the content including the watermark information, metadata, and signature are distributed to the mediator device.

  In the metadata created by the author device, the copyright information of the content, the right permission information to the delivery destination, the public key certificate of the author, the public key certificate of the delivery destination broker, etc. are described. Instead of the author's public key certificate included in the metadata created by the author device, the author's public key or the author's identifier may be used. It may be a public key or a distributor's identifier.

  Next, the intermediary device receives the distributed content with watermark information, metadata, and signature, and verifies the signature from the metadata and signature. If the signature is correct, the hash value of the signature embedded from the content with watermark information is detected and compared with the hash value of the signature of the metadata created by the author device included in the received metadata. If both the hash value of the signature detected from the watermark information-containing content and the hash value of the signature of the metadata created by the author device are equal, the content is used according to the metadata described in the metadata . Next, when the mediator device delivers content to the viewer device, it newly creates metadata for the content, applies an electronic signature to the created metadata using the mediator's private key, Distribute the created metadata and signature to the viewer device.

  In order for the intermediary device to verify the signature from the metadata and signature, the metadata and signature are verified using the public key certificate of the author included in the metadata. If the metadata includes a public key or identifier instead of the author's public key certificate, obtain the author's public key certificate from the third party authority's certificate authority device and obtain the author's public key. After verification, the signature is verified. As a result, it can be confirmed that the metadata has not been tampered with during the content distribution process.

  In the metadata created by the mediator device, the received metadata and signature, the copyright information of the content to be added, the right permission information for the distribution destination viewer, and the public key certificate of the distribution destination viewer are described. The rights permission information included in the metadata created by the intermediary device is controlled so that description beyond the scope of the rights permission information described in the received metadata cannot be made. For example, when the usage permission for 3 months is described in the received metadata, control is performed so that the usage permission for 1 year cannot be described in the created metadata.

  Also, the secret key used for signing the metadata created by the mediator device is a secret key corresponding to the mediator's public key included in the received metadata. As a result, only an intermediary device having a secret key corresponding to the public key described in the metadata can create new metadata.

  Next, the viewer apparatus receives the distributed watermarked content, metadata, and signature, and verifies the signature from the metadata and signature. If the signature is correct, the hash value of the signature embedded from the content with watermark information is detected and compared with the hash value of the signature of the metadata created by the author device included in the received metadata. If both the signature detected from the content and the signature of the metadata created by the author device are equal, the information described in the metadata is verified, and the content is determined according to the right permission information for the viewer. Use and watch.

  To verify the signature from the metadata and signature, the viewer device first verifies the metadata and signature using the mediator's public key certificate included in the metadata, and then verifies the signature included in the metadata. Using the author's public key certificate, the metadata and signature created by the author device included in the metadata are verified. If the metadata includes a public key or identifier instead of the author's or intermediary's public key certificate, obtain the author's or intermediary's public key certificate from the third party authority's certificate authority device. After verifying the public key of the author or intermediary, verify each signature. As a result, it can be confirmed that the metadata has not been tampered with during the content distribution process.

  In order for the viewer device to verify the information described in the metadata, it is necessary that the right permission information created by the mediator device included in the metadata does not exceed the scope of the right permission information created by the author device. Verify by comparing each license information.

  For example, a new right permission that is not described in the right permission information created by the author device is described in the right permission information created by the mediator device, or is written in the right permission information created by the author device. If the viewing permission period (for example, 6 months) exceeding the specified period (for example, 3 months) is described in the rights permission information created by the intermediary device, it is determined that the scope of the rights permission information is exceeded. .

  Further, when the viewer apparatus uses or views the content, if the secret key corresponding to the viewer's public key included in the metadata is not possessed, the content is controlled so that the content cannot be used or viewed.

  As a method of confirming possession of the private key, confirm that the encrypted data obtained by encrypting the arbitrary data with the viewer's public key and the decrypted data using the corresponding private key are equal to the arbitrary data. There is a way to do it. As another method, the content may be encrypted with the viewer's public key so that the content cannot be decrypted unless the private key corresponding to the viewer's public key is possessed. . Here, as a method of encrypting the content with the public key, the content is encrypted using the content key (common key encryption key), and the encrypted content key obtained by encrypting the content key with the viewer's public key is used as the content. The content may be distributed together, and the viewer may decrypt the content using the content key after decrypting the encrypted content key using the secret key corresponding to the public key.

  In each verification process, if the verification result is not correct, it is desirable to stop the subsequent processes. Further, it may be notified to the author device, the mediator device or the third party organization device as the distribution source.

  In addition, when the author device inserts digital watermark information, in addition to the hash value of the signature of the metadata, the copyright information of the content, the license information to the distribution destination, the author's public key certificate, the author's public key certificate, Any one or more of the information, the public key certificate of the distribution destination, and the information of the distribution destination may be inserted together as the digital watermark information.

  In addition, the mediator device adds the copyright information of the received watermark information, the copyright information of the content, the right permission information to the distribution destination, the public key certificate of the author, the information of the author, the public key certificate of the distribution destination, Any one or more of the distribution destination information may be inserted as digital watermark information.

  In addition, the author device, the mediator device, and the viewer device may store the metadata information in the database of the third party organization device or the database of each person device when distributing and receiving the content. good.

  Further, the intermediary device may be distributed to other intermediary devices if permitted by the right permission information. In that case, instead of the public key certificate of the distribution destination viewer, the public key certificate of the other intermediary of the distribution destination is described in the metadata, and the other intermediary device of the distribution destination verifies the signature. At this time, it is necessary to verify the signature of the mediator included in the metadata. When the viewer device receives the content across a plurality of mediator devices, the viewer device verifies all the signatures included in the metadata when verifying the signature, and verifies the information described in the metadata. Verifies that all of the license information does not exceed the scope of the license information of the distribution source.

  The author device may also serve as the mediator device. That is, the author device first distributes itself to itself, and after it becomes an intermediary device and adds information, it distributes to the viewer device or the next mediator device. This makes it possible to distribute content while giving different rights permission information to different viewers without reinserting the digital watermark information.

  According to the present invention, the public key certificate of the delivery destination and the right permission information are put in the metadata, and the hash value of the signature of the metadata is embedded in the content with a digital watermark, so that even when the mediator device is sandwiched, it is safe. It is possible to distribute content to the Internet. In addition, since the author device also serves as an intermediary device, it is possible to safely distribute content while giving different rights permission information to different viewer devices without re-inserting digital watermark information.

  FIG. 1 is a diagram showing a schematic configuration of the present embodiment. As shown in FIG. 1, the application form of this embodiment includes an author device 104 of the author 101, an intermediary device 105 of the mediator 102, and a viewer device 106 of the viewer 103.

  The author device 104, the mediator device 105, and the viewer device 106 according to the present embodiment have the configurations shown in FIGS. 4, 5, and 6, respectively. The CPU 401, the ROM 402, the input device 403, and the output device. 404, a communication device 405, and a memory 406. The CPU 401 is a device that controls the overall operation of each device. The input device 403 is a device, a keyboard, a mouse, or the like that inputs image data on a recording medium such as a DVD, CD-ROM, or HDD, or a communication medium such as wired or wireless. The output device 404 is a display that outputs video, a speaker that outputs audio, or the like. The communication device 405 is a device that performs communication and control with other processing devices via a network such as the Internet or an intranet, or a dedicated signal line such as SCSI or RS422. The memory 406 is a storage device that stores various processing programs and data such as image data for controlling each process.

  As shown in FIG. 4, the memory 406 of the author device 104 stores a watermark insertion unit 109, a distribution unit 110, a signature creation unit 111, and a metadata creation unit 112. A content storage area 407, a metadata storage area 408.

  The memory 406 of the mediator apparatus 105 stores a signature watermark verification unit 113, a metadata verification unit 114, a metadata generation unit 115, a signature generation unit 111, and a distribution unit 110 as shown in FIG. An area 407 and a metadata storage area 408 are provided.

  As shown in FIG. 6, the memory 406 of the viewer device 106 stores a signature watermark verification unit 113, a metadata verification unit 114, and a playback unit 115, and has a content storage area 407 and a metadata storage area 408. ing.

  Each processing unit of each device is implemented on each device by the CPU 401 executing a program stored in the memory 406. The program may be stored in advance in the memory 406 or an external storage device, or propagates on a removable storage medium that can be used by the information processing apparatus or a network or a network when necessary. It may be introduced via a communication medium such as a carrier wave that can be used by the information processing apparatus. Also, some or all of the functions of each device may be realized by hardware.

  The metadata creation unit 112 of the author device 104 creates metadata MA of the content 107 to be distributed. The metadata MA includes the copyright information of the content, the right permission information for the delivery destination mediator 102, the public key certificate of the author 101, the public key certificate of the delivery destination mediator 102, and the like.

  The copyright information of the content included in the metadata MA is information related to the copyright of the content. For example, content attribute information (content name, location, author, contributor, creation date, format, author ID, distribution destination) Enter one or more IDs etc. that are deemed necessary). Further, the right permission information to the distribution destination included in the metadata is the right information granted to the distribution destination. List at least one of the following restrictions, the selling price of the content, and the availability of copying. Also, the public key or identifier of the author 101 may be used instead of the public key certificate of the author 101, and the public key or identifier of the delivery destination broker 102 instead of the public key certificate of the delivery destination broker 102. It may be.

  After creating the metadata MA, the signature creation unit 111 applies a signature A to the metadata MA. As the secret key of the author 101 used for applying the signature A, a secret key corresponding to the public key of the author 101 included in the metadata MA is used.

  Next, the watermark insertion unit 109 inserts a hash value (for example, 64 bits) of the signature A with a digital watermark into the content 107 to be distributed to create a content 108 with watermark information. In addition to the hash value of the signature A, the watermark insertion unit 109 copyright information of the content included in the metadata, copyright permission information to the distribution destination, the author's public key certificate, the distribution destination public key certificate, The author's information, distribution destination information, etc. may be inserted together as a digital watermark.

  The distribution unit 110 distributes the created watermark information-containing content 108, the metadata MA, and the signature A to the mediator device 105 of the distribution destination mediator 102 described in the metadata.

  First, the mediator device 105 receives the distributed content information 108 including the watermark information, the signature A, and the metadata MA, and the signature watermark verification unit 113 verifies the signature A and the hash value of the signature detected from the content including the watermark information. And the hash value of signature A are compared, and if the verification result is not correct, the subsequent processing is stopped.

  The metadata verification unit 114 verifies the right permission information, the delivery destination ID, and the like included in the metadata MA. If the verification result is not correct, the subsequent processing is stopped. Further, it is verified whether the mediator 102 has the private key corresponding to the public key certificate of the mediator 102 included in the metadata MA. If the verification result is not correct, the subsequent processing is stopped.

  The metadata creation unit 112 creates metadata MB. The metadata MB includes a signature A, metadata MA, content copyright information, rights permission information for the distribution destination viewer 103, a public key certificate of the distribution destination viewer 103, and the like.

  The copyright information of the content included in the metadata MB is information related to the copyright of the content. For example, content attribute information (content name, location, author, contributor, creation date, format, distribution destination ID, etc.) , One or more items deemed necessary). Further, the right permission information to the distribution destination included in the metadata is the right information granted to the distribution destination. List at least one of the following restrictions, the selling price of the content, and the availability of copying. Further, the public key or identifier of the distribution destination may be used instead of the public key certificate of the distribution destination.

  After creating the metadata MB, the signature creation unit 111 applies a signature B to the metadata MB. As the secret key of the intermediary 102 used to apply the signature B, a secret key corresponding to the public key of the intermediary 102 included in the metadata MB is used.

  The distribution unit 110 distributes the received watermark information-containing content 108, the metadata MB, and the signature B to the viewer device 106 of the distribution destination viewer 103 described in the metadata.

  The viewer apparatus 106 receives the distributed content 108 including the watermark information, the signature B, and the metadata MB, and the signature watermark verification unit 113 verifies the signature B, verifies the signature A included in the metadata MB, and the watermark information. The signature hash value detected from the incoming content and the hash value of signature A are verified. If the verification result is not correct, the subsequent processing is stopped.

  The metadata verification unit 114 verifies the right permission information, the distribution destination ID and the right permission information included in the metadata MA, the distribution destination ID, and the like included in the metadata MB. If the verification result is not correct, the metadata verification unit 114 performs the subsequent processing. Discontinue. Also, it is verified whether the viewer 103 has the private key of the viewer 103 corresponding to the public key certificate of the viewer 103 included in the metadata MB. If the verification result is not correct, the subsequent processing is stopped.

  The reproduction / use unit 115 reproduces or uses the watermark information-containing content 108 in accordance with the right permission information for the viewer 103 included in the metadata MB. When it exceeds the scope of the right permission information for the viewer 103, the reproduction or use is stopped.

FIG. 2 is a flowchart showing a processing procedure of the signature watermark verification unit 113 of this embodiment.
In step 201, the distributed content including watermark information, signature, and metadata are received, and the process proceeds to step 202.
In step 202, the public key certificate included in the metadata is verified. If the verification is successful, the process proceeds to step 203. If the verification is unsuccessful, the subsequent processes are stopped and the process ends. If the metadata includes only the public key or identifier instead of the public key certificate, the public key certificate may be obtained from the third party organization apparatus and verified.
In step 203, the signature is verified using the public key verified in step 202. If the verification is successful, the process proceeds to step 204. If the verification is unsuccessful, the subsequent processing is stopped and the process is terminated.
In step 204, it is checked whether the metadata and signature created by the author device 104 or the mediator device 105 that have been passed are included in the metadata, and if included, the included metadata. The processing from step 202 is performed on the data and signature. If not included, it is determined that the metadata is metadata created by the author device, and the process proceeds to step 205.
In step 205, the watermark information is detected from the content including the watermark information. If it is detected, the process proceeds to step 206. If not detected, the subsequent processing is stopped and terminated.
In step 206, the watermark information detected in step 205 is compared with the hash value of the author's signature A. If they match, the process proceeds to step 207. If they do not match, the subsequent processing is stopped and terminated.
In step 207, the watermark information-containing content, signature, and metadata are transmitted to the next processing unit, and then the process ends.

FIG. 3 is a flowchart showing the processing procedure of the metadata verification unit 114 of this embodiment.
In step 301, the signature and metadata are received, and the process proceeds to step 302.
In step 302, the consistency verification of the right permission information included in the metadata is performed. If the verification is successful, the process proceeds to step 303. If the verification is unsuccessful, the subsequent processes are stopped and the process ends. Consistency verification of rights and license information is to verify all rights and rights information for whether or not each right and rights information has been granted a license that exceeds the scope of the rights and rights information created by the distributor device of the distribution source. It is processing.
In step 303, it is verified whether or not the private key corresponding to the public key of the final distributor included in the metadata is possessed. If the verification succeeds, the process proceeds to step 304. Then exit.
In step 304, after the signature and metadata are transmitted to the next processing unit, the processing is terminated.

  As described above, in the present embodiment, by including the public key certificate of the delivery destination in the metadata, it is possible to distribute the content safely even when the mediator device is sandwiched.

  In the above-described embodiment, when the verification result of each process is not correct, the subsequent process may be stopped, and the distribution source author, mediator, or third party organization may be notified. Specifically, the intermediary device 105 and the viewer device 106 are provided with a notification processing unit, and the metadata and watermark information-containing content and the notification information whose verification results are not correct are transmitted from the author device, mediator device or first What is necessary is just to transmit to a three-party engine apparatus.

  In addition, when the watermark is inserted by the watermark insertion unit 109, in addition to the hash value of the signature A, the copyright information of the content, the right permission information to the distribution destination, the author's public key certificate, the author's information, Of the public key certificate of the distribution destination, the information of the distribution destination, and the signature, one or more items determined to be necessary may be inserted together as a digital watermark.

  In the mediator device 105, before delivery by the delivery unit 110, for the content 108 with watermark information, the signature B, the copyright information of the content, the right permission information to the delivery destination, and the public key certificate of the author One or more of the documents, author information, public key certificate of the distribution destination, distribution destination information, signature, hash value of the signature, etc. deemed necessary may be inserted as digital watermark information. . Specifically, a watermark insertion unit may be provided between the signature watermark processing unit 113 and the distribution unit 110 of the mediator device 105, and the above information may be inserted into the content with watermark information as a digital watermark.

  In addition, the author device 104, the mediator device 105, and the viewer device 106 receive the metadata of the third party organization when the content is distributed by the distribution unit 110 or when the content is received by the signature watermark verification unit 113. It may be stored in a database, or each person may have a database, and metadata may be stored in this database.

  The author 101 may have both the author device 104 and the mediator device 105. Thus, the author first distributes the distribution destination to himself / herself, that is, the author 101 by the author device 104 to the mediator device 105, and then distributes to the viewer device 106 by the mediator device 105. In this way, it is possible to distribute content while giving different rights permission information to different viewer apparatuses 106 without re-inserting digital watermark information.

The schematic block diagram of the system of this invention. 2 is a flowchart showing details of a signature watermark verification unit 113 in FIG. 1. The flowchart which shows the detail of the metadata verification part 114 in FIG. The schematic block diagram of the author apparatus 104 in FIG. The schematic block diagram of the mediator apparatus 105 in FIG. The schematic block diagram of the viewer apparatus 106 in FIG.

Explanation of symbols

101: author, 102: mediator, 103: viewer, 104: author device, 105: mediator device, 106: viewer device, 107: content, 108: content with watermark information, 109: watermark insertion unit, 110: Distribution unit, 111: Signature creation unit, 112: Metadata creation unit, 113: Signature watermark verification unit, 114: Metadata verification unit, 115: Playback / use unit, 401: CPU, 402: ROM, 403: Input Device, 404: output device, 405: communication device, 406: memory, 407: content storage area, 408: metadata storage area

Claims (9)

In the distribution method of content distributed from the author device to the mediator device,
By author device,
Creating metadata including the public key certificate of the author, the public key certificate of the intermediary, and the license information;
Signing the metadata with the author's private key;
Inserting a hash value of the signature into the content with a digital watermark;
Transmitting the digital watermarked content, the metadata, and the signature to the mediator device. In a content delivery method for delivering content from a first mediator device to a second mediator device,
By the first intermediary device,
Receiving content and signatures and metadata;
Verifying the signature;
Verifying all signatures contained in the metadata;
Detecting digital watermark information from the content, comparing the detected watermark information with the hash value of the author's signature,
Verifying the license information contained in the metadata;
Creating metadata including the metadata, the signature, the public key certificate of the second intermediary serving as a distribution destination, and rights grant information;
Signing the created metadata with the first intermediary's private key;
Transmitting the content, the created metadata, and a signature created with the secret key of the first mediator to the second mediator device. In a method for distributing content distributed from an intermediary device to a viewer device,
By the mediator device,
Receiving content and signatures and metadata;
Verifying the signature;
Verifying all signatures contained in the metadata;
Detecting digital watermark information from the content, comparing the detected watermark information with the hash value of the author's signature,
Verifying the license information contained in the metadata;
Creating metadata including the metadata, the signature, the viewer's public key certificate, and rights grant information;
Signing the created metadata with the broker's private key;
Transmitting the content, the created metadata, and a signature created with the mediator's private key to the viewer apparatus. In a method for receiving content distributed from an intermediary device to a viewer device,
By the viewer device,
Receiving content and signatures and metadata;
Verifying the signature;
Verifying all signatures contained in the metadata;
Detecting digital watermark information from the content and comparing the detected watermark information with the hash value of the author's signature;
Verifying the license information contained in the metadata;
Using the content according to the right permission information. In the content delivery or reception method according to claim 2, claim 3, or claim 4,
When fraud is detected for the received content, the processing for the content is stopped, and the author device, the mediator device, or the third party device is notified of information related to the fraud. In the content delivery method according to claim 1, claim 2, or claim 3,
Copyright information of contents, copyright permission information to distribution destination, author's public key certificate, author's information, distribution destination public key certificate, distribution destination information, signature, hash value of the signature, There is a step of additionally inserting any one or more as digital watermark information. In the content delivery or reception method according to claim 1, claim 2, claim 3, or claim 4,
When distributing or receiving content, the method includes a step of storing metadata information in a database of a third party organization apparatus or a database held by each party apparatus. In the distribution method of content distributed from the author device to the mediator device,
According to the author device,
Creating metadata including the author's public key certificate and the first rights grant information;
Signing the metadata with the author's private key;
Inserting a hash value of the signature into the content with a digital watermark;
Creating metadata including the metadata, the signature, the public key certificate of the intermediary serving as a distribution destination, and second right permission information;
Signing the created metadata with the secret key of the author. In a content distribution system comprising an author device, an intermediary device, and a viewer device,
The author device is
Means for creating metadata including the author's public key certificate, the intermediary's public key certificate, and rights grant information;
Means for signing the metadata with the author's private key;
Means for inserting a hash value of the signature into the content with a digital watermark;
Means for transmitting the metadata, the signature, and the content to the mediator device;
The intermediary device is:
Means for receiving the metadata, the signature and the content;
Means for verifying the signature;
Means for verifying all signatures contained in the metadata;
Means for detecting digital watermark information from the content and comparing the detected watermark information with the hash value of the author's signature;
Means for verifying the license information contained in the metadata;
Means for creating new metadata including the metadata, the signature, the viewer's public key certificate, and rights grant information;
Means for applying a new signature to the created new metadata with the mediator's private key;
Means for transmitting the metadata, the signature, and the content to the viewer device;
The viewer device is:
A means of receiving content and new signatures and new metadata;
Means for verifying the new signature;
Means for verifying all signatures included in the new metadata;
Means for detecting digital watermark information from the content and comparing the detected watermark information with the hash value of the author's signature;
Means for verifying the license information contained in the new metadata;
Means for reproducing the content in accordance with the right permission information.

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