Access control method, access control system, metadata controlling device, and transmitting apparatus

The present invention relates to a method of controlling access to content from metadata in digital broadcasting.

Broadcasting systems based on home servers achieves program viewing that is not restricted by airtime, with a provision of a program storage device and a communication connecting function in a receiving device. Further, a content provider provides program-related information, called metadata, to achieve various broadcast services such as highlight program viewing. For example, such services include a service to allow a viewer to see only hitting scenes of a hitter as a digest of a baseball broadcast program. This service is achieved by a content provider who produces metadata including a program name indicative of a baseball broadcast program and information indicative of starting time points of all hitting scenes of the hitter and provides the metadata to a viewer. From the viewpoint of producing attractive metadata inexpensively, it is considered that metadata are produced not only by a content provider, but also by a network provider, a third party, or a user.

Meanwhile, falsification of metadata or production of unauthorized metadata may cause program use against content provider's intention, such as allowing a program to be viewed without any commercials or connecting scenes in a plurality of programs so as to generate another program. Accordingly, in order to prevent rampancy of unauthorized metadata, falsification of metadata should be prevented, and a content provider should be able to specify metadata permitted to be used for each program.

A reference discloses an outline of the standard of ARIB (Association of Radio Industries and Businesses) STD-B38 (Coding, Transmission and Storage Specification for Broadcasting Systems Based on Home Servers) and particularly illustrates a concept of broadcasting systems based on home servers (Reference: Standard outline (broadcasting field), Number of Standard: ARIB STD-B38, Name of Standard: Coding, Transmission and Storage Specification for Broadcasting Systems Based on Home Servers, [online], Association of Radio Industries and Businesses, [searched on Jan. 29, 2004], the Internet <URL: http://www.arib.or.jp/tyosakenkyu/kikaku_hoso/hoso_std-b038.html>).

The standard of ARIB STD-B38 defines a description method of metadata for a program in an XML (Extensible Markup Language) format. The standard of ARIB STD-B38 formulates the definitions not only for describing additional information on content in metadata and displaying the additional information on a playback terminal, but also for describing information for playback control such as a partial playback of content based on a description in metadata. With use of a playback device having a function of playing back content based on metadata, the content can partially be played back, or a digest of the content can be defined and played back without editing the content.

Here, since metadata are described by XML, anyone can readily generate metadata. Thus, anyone can readily generate a digest of content if the content is accessible. Accordingly, it has been necessary to provide an access control to content, for example, so that access is permitted from metadata produced by an author A but is not permitted from metadata produced by an author B.

An object of the present invention is to provide an access control method of controlling acceptance or rejection of access to content according to a producer of metadata in broadcasting systems based on home servers in which metadata and content are distributed so as to achieve a function of a playback control of the content by the metadata.

Another object of the present invention is to provide an access control system for performing the above access control method.

Still another object of the present invention is to provide a metadata controlling device for controlling propriety of access to content according to a producer of metadata.

Still another object of the present invention is to provide a transmitting apparatus for allowing a receiving apparatus to control propriety of access to content according to a producer of metadata.

According to the present invention, there is provided an access control method characterized by comprising:

a producer information embedding step of embedding producer information indicating a producer of metadata produced for content in the metadata;

a step of embedding an identifier indicating which metadata are accessible to the content in license information required to play back the content; and

an access propriety control step of comparing the producer information with the identifier to control propriety of access to the content from the produced metadata.

Further, according to the present invention, there is provided an access control system characterized by comprising:

producer information embedding means for embedding producer information indicating a producer of metadata produced for content in the metadata;

identifier embedding means for embedding an identifier indicating which metadata are accessible to the content in license information required to play back the content; and

access propriety control means for comparing the producer information with the identifier to control propriety of access to the content from the produced metadata.

Further, according to the present invention, there is provided a metadata controlling device used in a content receiving part having a function of receiving and playing back content and a function of receiving an identifier which indicates which metadata are accessible to the content and is embedded in license information required to play back the content, characterized by comprising:

a function of receiving metadata produced for the content and producer information which indicates a producer who has produced the metadata and is embedded in the produced metadata; and

an access propriety controlling function of obtaining the identifier from the content receiving part and comparing the producer information in the metadata with the identifier to control propriety of access to the content in the content receiving part from the produced metadata.

Furthermore, according to the present invention, there is provided a transmitting apparatus having a content transmitting device for transmitting content to a receiving apparatus and a metadata transmitting device for transmitting metadata produced for the content to the receiving apparatus, characterized in that;

said metadata transmitting device has a function of transmitting the produced metadata to the receiving apparatus in a state such that producer information indicating a producer of the metadata is embedded in the produced metadata,

said content transmitting device has a function of transmitting license information required to play back the content to the receiving apparatus in a state such that an identifier indicating which metadata are accessible to the content is embedded in the license information, and

said transmitting apparatus is operable to allow the receiving apparatus to control propriety of access to the content from the produced metadata by comparison of the producer information received from said metadata transmitting device with the identifier received from said content transmitting device.

According to the present invention, it is possible to determine access propriety to content from metadata by comparing producer information (signature value) indicating a producer of the metadata with an identifier (metadata access control descriptor) embedded in license information required to play back the content.

FIG. 1 is a block diagram of an access control system according to a first embodiment of the present invention;

FIG. 2 is a diagram showing pre-signature metadata generated by a metadata producer 1 in a metadata generating device of the access control system of FIG. 1 ;

FIG. 3 is a diagram showing metadata with an author's signature in the metadata generating device of the access control system of FIG. 1 ;

FIG. 4 is a block diagram of an access control system according to a second embodiment of the present invention;

FIG. 5 is a diagram showing signed metadata additionally edited in a metadata controlling device of the access control system of FIG. 4 ;

FIG. 6 is a block diagram of a metadata generating device in the access control system of FIG. 4 ;

FIG. 7 is a block diagram of the metadata controlling device in the access control system of FIG. 4 ;

FIG. 8 is a block diagram of a transmitting device in a content generator of the access control system of FIG. 4 ;

FIG. 9 is a block diagram of a content receiving device in the access control system of FIG. 4 ; and

FIG. 10 is a diagram explanatory of metadata access control descriptors used in the access control system of FIG. 4 .

In the following embodiment of the present invention, there is described an example in which producer information which is embedded in metadata and indicates a producer who has produced the metadata is a digital signature of the producer. However, the producer information is not limited to a digital signature and may be other information indicating a producer who has produced the metadata. Here, a producer who has produced metadata is a generator who has generated an instance (entity) itself of the metadata in the metadata or a producer who has added and edited the metadata.

Specifically, in the following embodiment, a digital signature (XML signature) of a generator who has generated an instance (entity) itself of metadata, which is defined by ARIB STD-B38, in the metadata (or a producer who has added and edited the metadata) is embedded as producer information in the metadata to identify the generator who has generated the metadata (or the producer who has added and edited the metadata). Meanwhile, an identifier for determining which metadata is accessible to content is embedded in the content. Propriety of access to the content from the produced metadata is controlled by comparing the digital signature (XML signature) and the identifier with each other.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an access control system according to a first embodiment of the present invention. This access control system serves to control access to content from metadata.

This access control system has a metadata generating device 2 used for generating metadata 3 A for content 6 A, which has already been generated. That is, a metadata producer 1 having a metadata generating device 2 generates metadata 3 A for content GA, which has already been generated, with the metadata generating device 2 .

Here, a metadata access control descriptor 7 A indicating which metadata are permitted to access the content 6 A is embedded in the content 6 A. Typically, the metadata access control descriptor 7 A indicates a producer of metadata that are permitted to access the content 6 A. This is one of the features of the present invention.

FIG. 2 shows metadata (pre-signature metadata) generated by the metadata producer 1 . In the pre-signature metadata, for example, information indicating start time points of all hitting scenes of a hitter in the aforementioned baseball broadcast program is inserted as an instance of the metadata into one of product portions 13 of the producer.

Referring back to FIG. 1 , the metadata producer 1 has a public key certificate to verify the producer and a secret key corresponding to the public key certificate. When generation of the metadata 3 A is completed, the metadata producer 1 adds an XML signature 4 A defined by XML-Signature and a public key certificate 5 A used in the signature into the metadata 3 A with the metadata generating device 2 so as to generate metadata with a producer signature.

FIG. 3 shows the aforementioned metadata 3 A with the producer signature. The public key certificate 5 A of the signer is embedded in the signature 4 A of the producer 1 , which is in an XML format, in a form in which binary data are base64-encoded.

Referring back to FIG. 1 , the content 6 A is distributed to a user via a broadcasting network 11 , which serves as a communication means for broadcasting. The metadata 3 A are distributed to the user via a network (telecommunication network such as the Internet) 10 . The user has a metadata controlling device 8 connected to the network 10 for obtaining the metadata 3 A distributed from the metadata generating device 2 as metadata 3 B and a content receiving device 9 for obtaining the content 6 A from the broadcasting network 11 as content 6 B. The content receiving device 9 also has a content playback function. The user accesses the distributed metadata 3 B (equivalent to 3 A) with use of the metadata controlling device 8 . If the metadata 3 B is accessible to the content 6 B (equivalent to 6 A), the user can view an image digest of the content 6 B or the like based on the metadata 3 B.

The above example shows a method of distributing the content 6 A via the broadcasting network 11 and distributing the metadata 3 A via the network 10 to the user. However, the content 6 A may be distributed via the network, and the metadata 3 A may be distributed via the broadcasting network. Further, both of the content 6 A and the metadata 3 A may be distributed via the broadcasting network. Alternatively, both of the content 6 A and the metadata 3 A may be distributed via the network.

In this case, when the metadata controlling device 8 is to gain access to the content 6 B from the metadata 3 B, it verifies the signature 4 A of the metadata producer, which has been provided to the metadata 6 B, to confirm that the metadata 3 B have not been falsified. Next, the metadata controlling device 8 obtains a value of a subject area at which information on an owner of a public key certificate is described in the public key certificate 5 A of the metadata producer, and identifies the producer of the metadata 3 A. Subsequently, the metadata controlling device 8 accesses the content receiving device 9 to obtain the metadata access control descriptor 7 A in the content 6 B. The metadata controlling device 8 compares the metadata access control descriptor 7 A with the information on the owner of the public key certificate (the subject of the public key certificate defined by RFC3280) to determine whether the metadata is accessible to the content.

Specifically, when the information on the owner of the public key certificate (the subject of the public key certificate defined by RFC3280) is described in the metadata access control descriptor 7 A as a producer of metadata that are permitted to access to the content, the metadata controlling device 8 is permitted to access the content 6 B from the metadata 3 B, so that an image digest of the content 6 B or the like can be viewed based on the metadata 3 B.

Here, when the metadata access control descriptor 7 A describes that any metadata producer is accessible to the content, all metadata producers can view an image digest of the content 6 B based on his/her metadata without restriction.

Further, when the information on the owner of the public key certificate (the subject of the public key certificate defined by RFC3280) is identified (or specified) as a producer of metadata who is described in the metadata access control descriptor 7 A, the metadata controlling device 8 is also permitted to access the content 6 B from the metadata 3 B, so that an image digest of the content 6 B or the like can be viewed based on the metadata 3 B.

Any digital signature may be employed as long as it can specify a signer as a producer based on public key infrastructure (PKI) technology.

FIG. 4 shows an access control system according to a second embodiment of the present invention. This access control system further includes a content generating device 22 for generating the aforementioned content 6 A ( FIG. 1 ), and a metadata controlling device 29 and a content receiving and transmitting device 30 , which are connected between a metadata generating device 2 ( FIG. 1 ) and a metadata controlling device 8 ( FIG. 1 ) and between the content generating device 22 and a content receiving device 9 ( FIG. 1 ). In the illustrated example, the metadata controlling device 29 and the content receiving and transmitting device 30 are connected to the metadata generating device 2 and the content generating device 22 via a network 25 , and connected to the metadata controlling device 8 and the content receiving device 9 via a network 10 and a broadcasting network 11 .

In this case, the same network as the network 10 may be used as the network 25 . Alternatively, the network 10 and the broadcasting network 11 may be used for connections between the metadata generating device 2 and the metadata controlling device 29 and between the content generating device 22 and the content receiving and transmitting device 30 instead of the network 25 .

In this access control system, the content receiving and transmitting device 30 has a function of the content receiving device 9 shown in FIG. 1 , which obtains the content 6 A from the network 25 as content 6 A′ (and also has a content playback function), and a function of a transmitting device to send the content 6 A′ via the broadcasting network 11 . In succession to the content receiving and transmitting device 30 , the content receiving device 9 obtains the content 6 A′ from the broadcasting network 11 as content 6 B.

The metadata controlling device 29 obtains metadata 3 A from the network 25 as metadata 3 A′. The metadata controlling device 29 obtains metadata 3 A from the network 25 as metadata 3 A′. As with the metadata controlling device 8 described in FIG. 1 , when a metadata producer 1 is described or identified (or specified) in a metadata access control descriptor 7 A of the content 6 A as a producer of metadata that are permitted to access to the content, the metadata controlling device 29 is permitted to access the content 6 A′ from the metadata 3 A′. A user (metadata producer 34 ) of the metadata controlling device 29 and the content receiving and transmitting device 30 can view an image digest of the content 6 A′ or the like based on the metadata 3 A′.

The metadata controlling device 29 also has a function of sending the metadata 3 A′ via the network 10 . In succession to the metadata controlling device 29 , the metadata controlling device 8 obtains the metadata 3 A′ from the network 10 as metadata 3 B. As described in connection with FIG. 1 , when the metadata producer 1 is described or identified (or specified) in the metadata access control descriptor 7 A of the content 6 B as a producer of metadata that are permitted to access the content, a user of the metadata controlling device 8 and the content receiving device 9 is also permitted to access the content 6 B from the metadata 3 B, so that the user can view an image digest of the content 6 B or the like based on the metadata 3 B.

In this access control system, it is assumed that the metadata producer 1 generates the metadata 3 A for the content 6 A with the metadata generating device 2 , and that the metadata producer 34 additionally edits the metadata 3 A into the metadata 3 A′ with the metadata controlling device 29 .

FIG. 5 shows signed metadata 3 A′ in an XML format in a case where the metadata producer 34 additionally edits the metadata 3 A with the metadata controlling device 29 . In this case, product portions 13 ( FIG. 2 ) of the metadata producer 1 and product portions 37 of the metadata producer 34 are mixed in the signed metadata 3 A′ in an XML format, which are produced by two of the metadata producer 1 and the metadata producer 34 . The XML signatures of the metadata producer 1 and the metadata producer 34 are embedded in the metadata 3 A′ as a signature 4 A ( FIG. 2 ) of the metadata producer 1 and a signature 39 of the metadata producer 34 .

In FIG. 4 , however, when an owner (metadata producer 34 ) of a public key certificate in the signature 39 of the XML signature is not described or identified (or specified) in the metadata access control descriptor 7 A of the content 6 A′ as a producer of metadata that are permitted to access to the content, the metadata controlling device 29 is not permitted to access the content 6 A′ from the metadata 3 A′. Accordingly, an image digest of the content 6 A′ or the like cannot be viewed based on the metadata 3 A′.

Thus, even if the metadata producer 34 adds metadata in the product portions 37 for access to the content 6 A′, which has been received by the content receiving and transmitting device 30 , with the metadata controlling device 29 , it is possible to achieve an access control to content from metadata such that the metadata is inactivated unless authorization was provided when the metadata access control descriptor 7 A was generated by the content generating device 22 .

Here, in FIG. 4 , it is assumed that a receiving apparatus is formed by a combination of the metadata controlling device 29 and the content receiving and transmitting device 30 or by a combination of the metadata controlling device 8 and the content receiving device 9 . Further, in FIG. 4 , it is assumed that a transmitting apparatus has a content transmitting device (content generating device 22 ) for sending content to the receiving apparatus and a metadata transmitting device (metadata generating device 2 ) for sending metadata produced for the content to the receiving apparatus.

In this case, the metadata transmitting device (metadata generating device 2 ) has a function of sending the produced metadata to the receiving apparatus in a state such that a digital signature of a producer who has produced the metadata is embedded in the produced metadata. The content transmitting device (content generating device 22 ) has a function of sending license information required to play back the content to the receiving apparatus in a state such that an identifier indicating which metadata are permitted to access the content is embedded in the license information. Further, the transmitting apparatus is configured so that the receiving apparatus can control propriety of access to the content from the produced metadata by comparison of the digital signature received from the metadata transmitting device (metadata generating device 2 ) and the identifier received from the content transmitting device (content generating device 22 ).

Next, respective portions in the embodiment shown in FIG. 4 will be described in detail.

(The Metadata Generating Device 2 )

Referring to FIG. 6 , the metadata generating device 2 is formed of an information processing unit such as a personal computer to which an IC (Integrated Circuit) card reader/writer 45 is connected. The metadata generating device 2 is formed by a metadata generating part 41 and a metadata sending part 42 , which are provided by software, for example. The metadata generating device 40 has a function of generating metadata 3 A ( FIG. 4 ) corresponding to content 6 A ( FIG. 4 ), a function of providing a digital signature to the generated metadata 3 A, and a function to access an IC card 46 , in which a public key certificate and a secret key used for a digital signature are stored. The IC card reader/writer 45 is connected to the metadata generating device.

The metadata generating part 41 has a function of generating metadata 3 A corresponding to the content 6 A, and is configured by software having a signature generating part 43 as a function of adding a digital signature to the generated content 6 A. Further, the metadata generating part 41 has a content playback controlling part 44 for playing back the content 6 A with use of the generated metadata 3 A.

The metadata sending part 42 has a function of transferring the metadata 3 A generated by the metadata generating part 41 to the metadata controlling device 29 ( FIG. 4 ) via the telecommunication network 25 ( FIG. 4 ) such as the Internet.

The signature generating part 43 has a function of providing a digital signature to the generated metadata 3 A and executes a signature by generating a signature document in an XML-Signature format, which is a standard of W3C, from a document to be signed, generating a hash value for signature, generating a signature value with the IC card 46 via the IC card reader/writer 45 , and embedding the generated signature value in the XML signature document. Further, the signature generating part 43 also has a function of embedding a public key certificate of a signer, which is stored in the IC card 46 , in the document to be signed.

The IC card 46 can store a secret key and a public key certificate therein and has a function of making an encryption calculation therein. When a hash value of a document to be signed is received via the IC card reader/writer 45 , the hash value is encrypted to generate a signature value, which is returned to the signature generating part 43 via the IC card reader/writer 45 .

The IC card reader/writer 45 has a function of reading information in the IC card 46 in response to a command from an information processing unit such as a personal computer and a function of commanding the IC card 46 to make an encryption calculation for a digital signature using a key stored in the IC card 46 .

The content playback controlling part 44 has a function of commanding the content generating device 22 ( FIG. 4 ) to partially play back content according to the metadata 3 A.

(The Metadata Controlling Device 29 (or 8 ))

Referring to FIG. 7 together with FIG. 4 , the metadata controlling device 47 is formed of an information processing unit such as a personal computer to which an IC card reader/writer 52 is connected. The metadata controlling device 47 is formed by a metadata editing part 48 including a signature generation and verification function part 49 and a content playback controlling part 50 , and a metadata receiving and transmitting part 51 , which are provided by a software program.

The IC card reader/writer 52 and an IC card 53 are the same as those connected to the metadata generating device 40 .

The metadata editing part 48 has a function of editing metadata 3 A′ (or 3 B), a function of providing a digital signature to the edited portion with use of the signature generation and verification function part 49 , the IC card reader/writer 52 , and the IC card 53 , a function of verifying a signature and a certificate provided to the metadata 3 A′ (or 3 B), and a content playback controlling part 50 for controlling playback of the content 6 A′ (or 6 B).

The signature generation and verification function part 49 has a function of generating a signature as with the metadata generating device 2 , a function of verifying a signature value of the provided metadata, and a function of verifying a certificate.

The content playback controlling part 50 has a function of commanding the content receiving and transmitting device 30 (or the content receiving device 9 ) to partially play back the content 6 A′ (or 6 B) according to the metadata 3 A′ (or 3 B). Further, the content playback controlling part 50 has a function of obtaining a metadata access control descriptor 7 A, which is utilized to determine whether the metadata 3 A′ (or 3 B) is accessible to the content 6 A′ (or 6 B) at the time of playback, from the content 6 A′ (or 6 B). The content playback controlling part 50 has a function of obtaining a public key certificate of a metadata producer from a metadata producer signature embedded in the metadata 3 A′ (or 3 B) and identifying a signer from an owner of the public key certificate. The content playback controlling part 50 has a function of comparing the identified signer with the obtained metadata access control descriptor 7 A to determine propriety of access to the content 6 A′ (or 6 B).

(The Transmitting Device in the Content Generating Device 22 )

Referring to FIG. 8 together with FIG. 4 , the transmitting device in the content generating device 22 is formed by a content generating means 57 having a content storage unit 54 for storing content therein, an encoding part 55 , and a scrambling part 56 , a key generating means 58 having a content key generating part 59 for generating a content key Kc, a metadata access control information generating part 60 , and a Kc transmission ECM/EMM generating part 61 for generating license information (Kc transmission ECM (Entitlement Control Message)/EMM (Entitlement Management Control Message)) required to play back content, and a multiplexing means 63 for multiplexing encrypted content generated by the content generating means 57 and a key generated by the key generating means 58 .

The content storage unit 54 is formed by a storage device such as a hard disk for storing the content 6 A of images, sounds, or data.

The encoding part 55 is formed by an encoding device for encoding images, sounds, or data in MPEG (Motion Picture Experts Group)-2 TS (Transport Stream).

The content key generating part 59 generates an encryption key (content key Kc) for encrypting content with a common key cryptography for each content, assigns a content identification for identifying the content, and manages the content key for each content identification.

The scrambling part 56 encrypts encoded content with the content key generated by the content key generating part 59 and generates encrypted content.

The metadata access control information generating part 60 generates a metadata access control descriptor 7 A for permitting use of content 6 A to metadata. The metadata access control descriptor 7 A is formed by a metadata producer type indicative of a metadata producer identification, which is an identification code of a metadata producer, and an attribute of a metadata producer (such as a metadata producer who is also a content provider, a professional metadata producer, or a user).

The Kc transmission ECM/EMM generating part 61 generates a Kc transmission ECM or a Kc transmission EMM in a section format defined by ARIB-STDB25, “Access Control System for Digital Broadcasting,” which includes a content key Kc, metadata access control information (metadata access control descriptor 7 A), and a work key or a master key 62 . Specifically, in the Kc transmission ECM/EMM generating part 61 , license information required for the metadata access control information (metadata access control descriptor 7 A) to play back content is embedded in a Kc transmission ECM or a Kc transmission EMM. The Kc transmission ECM performs an encryption with a work key 62 , and the Kc transmission EMM performs an encryption with a master key 62 . The master key 62 is an encryption key which is provided for each receiving device with a common key cryptography. The work key 62 is an encryption key which is provided for each unit such as a carrier with a common key cryptography, is also an encryption key common to receiving devices which are to receive a Kc transmission ECM, and is an encryption key to group respective receiving devices. That is, the Kc transmission ECM is used when Kc is broadcasted to receiving devices having a common work key. The Kc transmission EMM is used when Kc is distributed individually to respective receiving devices.

When a Kc transmission ECM/EMM (license information) is sent by broadcasting, a multiplexing part 64 of the multiplexing means 63 multiplexes and modulates the encrypted content of the content generating means 57 and the Kc transmission ECM/EMM encrypted with a work key, and sends them as broadcasting.

Here, when Kc is distributed individually to respective receiving devices, a Kc transmission EMM (license information) is individually distributed via a telecommunication network using TCP/IP (Transmission Control Protocol/Internet Protocol).

(The Transmitting Device in the Content Receiving and Transmitting Device 30 )

The transmitting device in the content receiving and transmitting device 30 also has the same arrangement as the transmitting device in the content generating device 22 shown in FIG. 8 . The content storage unit 54 in the content generating means 57 stores content (images, sounds, or data) received from the content generating device 22 by the receiving device in the content receiving and transmitting device 30 .

(The Content Receiving Device 9 )

Referring to FIG. 9 together with FIG. 4 , the content receiving device 9 is formed by a content decoding means having a descrambling part 67 and a decoding part 69 , a security module 74 having a Kc transmission ECM/EMM decoding part 70 , a content key storage unit 72 , and a metadata access control information storage unit 73 , and a separating means for separating encrypted content 66 and key information from each other.

The security module 74 is a tamper-proof module which prevents information from being falsely fetched from an exterior of the module and is formed by an IC card or the like. The security module 74 is strictly issued and managed by a trusted third party.

A separating part 65 demodulates the received broadcasting and separates it into encrypted content 66 and Kc transmission ECM/EMM 76 at an MPEG-2 TS level.

The Kc transmission ECM/EMM decoding part 70 decrypts and decodes the received Kc transmission ECM with a work key 71 and the received Kc transmission EMM with a master key 71 , fetches a content key (Kc) 68 and metadata access control information (metadata access control descriptor 7 A) 75 , and stores them in the content key storage unit 72 and the metadata access control information storage unit 73 . Thus, the content key (Kc) 68 and the metadata access control information (metadata access control descriptor 7 A) 75 are stored safely in the security module 74 .

At that time, the content key storage unit 72 stores the content key 68 for each content identification.

The metadata access control information storage unit 73 stores the metadata access control information (metadata access control descriptor 7 A) 75 for each content identification.

The descrambling part 67 decrypts and decodes the encrypted content with the content key 68 obtained from the security module 74 .

The decoding part 69 decodes the received content encoded in MPEG-2 TS and fetches audiovisual information or digital data as the content 6 B.

(The Receiving Device in the Content Receiving and Transmitting Device 30 )

The receiving device in the content receiving and transmitting device 30 also has the same arrangement as the content receiving device shown in FIG. 9 and receives content (images, sounds, or data) as content 6 A′ from the content generating device 22 .

(Others)

In FIG. 4 , the network 25 and the network 10 transmit metadata via a telecommunication network such as the Internet.

The broadcasting network 11 distributes content between image playback devices via an existing broadcasting network.

Next, operation in a case where the user of the metadata controlling device 8 and the content receiving device 9 also adds metadata in the embodiment shown in FIG. 4 will be described below.

In FIG. 4 , content itself is produced in advance and stored in the content generating device 22 . FIG. 8 is a detailed block diagram of the content generating device 22 shown in FIG. 4 .

In FIG. 8 , content 6 A ( FIG. 4 ) is stored in the content storage unit 54 . The content generating device 22 encrypts content, generates an encryption key (content key Kc) for each content in order to transmit it to the content receiving device 9 (or the content transmitting and receiving device 30 ), assigns a content identification in order to identify the content, and manages a content key for each content identification.

The content is read from the content storage unit 54 and encoded in MPEG-2 TS (Transport Stream) by the encoding part 55 . With use of the content key generated in the content key generating part 59 , the encoded content is encrypted by the scrambling part 56 to generate encrypted content.

In order to achieve an access control to content from metadata, it is necessary to embed an access control parameter in content. Accordingly, the metadata access control information generating part 60 generates a metadata access control descriptor 7 A as an access control parameter. The metadata access control descriptor 7 A is formed by a metadata producer identification, which is an identification code of a metadata producer, and a metadata producer type indicating an attribute of the metadata producer (a metadata producer who is also a content provider, a professional metadata producer, a user, or the like).

Data structure of the metadata access control descriptor 1 describing a metadata producer type is shown in an upper table of FIG. 10 . Metadata structure of the metadata access control descriptor 1 describing a metadata producer identification is shown in a lower table of FIG. 10 .

In FIG. 8 , the Kc transmission ECM/EMM generating part 61 encrypts the generated content identification, the content key, and the metadata access control information into a Kc transmission ECM or a Kc transmission EMM with a work key or master key 62 in a section format defined by ARIB-STDB25, “Access Control System for Digital Broadcasting.” The master key 62 is an encryption key provided for each receiving device with a common key cryptography, and the work key 62 is an encryption key provided for each unit such as a carrier with a common key cryptography.

Meanwhile, the metadata producer 1 of FIG. 4 generates metadata 3 A for content 6 A with the metadata generating device 2 . FIG. 6 is a detailed block diagram of the metadata generating device 1 .

In FIG. 6 , the metadata producer 1 generates metadata 3 A for content 6 A with the metadata generating part 41 of the metadata generating device 2 . The generated metadata are a document in an XML format in accordance with the definition of ARIB STD-B38 as shown in FIG. 2 . After the metadata producer 1 generates the metadata in an XML format as shown in FIG. 2 , the metadata producer 1 provides a metadata producer signature 4 A (in accordance with an XML-Signature) for the generated metadata as shown in FIG. 3 .

In FIG. 3 , a metadata producer public key certificate 5 A of the producer is included in the metadata producer signature 4 A. The metadata after signature becomes signed metadata 3 A in an XML format. When the entire document or the product portions 13 of the producer 1 are to be signed, the signed XML document is embedded as a signature 4 A of the producer in the metadata in a format according to XML-Signature Syntax and Processing. Further, a public key certificate of a signer is embedded as a public key certificate 5 A of the signer in the signature 4 A of the producer according to the standard of the XML-Signature for certificates.

In FIG. 4 , the metadata 3 A and the content 6 A produced by a first producer 1 is transferred via the network 25 to a second producer (referred to as a metadata producer 34 ), who is a content provider.

When the second producer 34 receives the metadata as 3 A′ from the first producer 1 , the second producer 34 adds product portions 37 of the metadata producer 34 to the metadata 3 A′ as shown in FIG. 5 .

In FIG. 5 , signature processing is conducted on portions generated by the metadata producer 34 after the addition, and a signature 39 of the metadata producer 34 is provided to the metadata. The signature 39 of the metadata producer 34 contains a metadata producer public key certificate, which is a public key certificate of the second producer 34 . In this manner, the signature 39 of the metadata producer 34 is embedded in the metadata.

In FIG. 4 , content 6 A′ (equivalent to 6 A) and metadata 3 A′ produced by the metadata producer 34 are distributed via the network 10 and the broadcasting network 11 so that the metadata 3 A′ is distributed as metadata 3 B to the metadata controlling device 8 , which is a user's terminal, and that the content 6 A′ is distributed as the content 6 B to the content receiving device 9 . The user verifies the signature 4 A of the metadata producer, which is a signature of the metadata producer 1 , and the signature 39 of the metadata producer, which is a signature of the metadata producer 34 ( FIG. 5 ), each of which has been added to the distributed metadata 3 B, and confirms that the metadata 3 B have not been falsified. Then, the user can generate a metadata addition in product portions of the user in the metadata 3 B, as with the product portions 37 in FIG. 5 , and can add his/her signature as with the signature 39 in FIG. 5 in the product portions of the user in the metadata 3 B.

In this case, the user plays back a digest of the content 6 B using the metadata 3 B including his/her metadata addition. At that time, fragments of the content 6 B to be played back are described in the metadata 3 B between tags <SegmentInformation . . . > and </SegmentInformation> according to ARIB STD-B38. The content receiving device 9 is commanded to play back a digest of the content 6 B according to the fragment information. Playback is performed after checking access control information to the content 6 B from the metadata 3 B, which is one of the most important features of the present invention. Acceptance or rejection of access to the content 6 B from the metadata 3 B is determined in the following procedures.

Procedure 1: A first signature (a signature 4 A of the metadata producer 1 ), a second signature (a signature 39 of the metadata producer 34 ), and a third signature (a signature of a user using the metadata controlling device 8 and the content receiving device 9 ), which are included in the metadata 3 B, are verified. Simultaneously, certificates required for the verification of the signatures are also verified.

Procedure 2: A person who has generated a portion in the metadata to be used is identified from a signature added in that portion. At that time, owner's name and owner's organization are specified from an owner of a public key certificate of a metadata producer that is contained in the first to third signatures (signature document in an XML signature format). Owner's attributes of a public key certificate are represented in a format called DN (Distinguished Name). Owner's name is registered in a value cn, and owner's organization is registered in a value ou. The same naming convention as the metadata access control identification of FIG. 10 is applied to the value cn, and the same naming convention as the metadata access control type of FIG. 10 is applied to the value ou.

Procedure 3: Meanwhile, access control information according to the two tables of FIG. 10 , which was generated in the metadata access control information generating part 60 ( FIG. 8 ) of the content generating device 22 at the time of generation of the content, is distributed as a metadata access control identifier 7 A to the content receiving device (playback device) 9 together with the content 6 A. The metadata controlling device 8 makes an inquiry to the content receiving device (playback device) 9 to obtain the metadata access control identifier 7 A.

Procedure 4: At that time, in response to a request from the metadata controlling device 8 , the content receiving device (playback device) 9 of FIG. 9 fetches metadata access control information 75 (metadata access control identifier 7 A) from the metadata access control information storage unit 73 and returns it to the metadata controlling device 8 .

Procedure 5: A metadata access control identification and a metadata access control type of the metadata access control descriptor 7 A returned from the content receiving device (playback device) 9 are compared with owner attributes cn and ou of certificates of three producers who produced the metadata to be used. An access control is performed by determining whether the owner attributes cn and ou of the certificates of the three producers match the metadata access control identification and the metadata access control type of the metadata access control descriptor 7 A.

If at least one of the owners of the certificates of the three producers is described in the metadata access control descriptor 7 A, access to the content 6 B is permitted from the information in the metadata 3 B which was produced by the owner. When the access is permitted, the content receiving device (playback device) 9 is commanded to perform a partial playback of the content 6 B or to display other information according to the information of the permitted metadata 3 B. The content receiving device (playback device) 9 performs a partial playback of the content 6 B according to the instructions.

As described above, the embodiment of the present invention has features in that, with regard to separately distributed metadata and contents in a format defined by ARIB STD-B38, propriety of access to content from metadata is controlled by comparing information of an owner of a public key certificate of a signer of the metadata with a metadata access control descriptor embedded in the content.

According to the embodiment of the present invention, it is possible to determine access propriety to content from metadata by comparing information of an owner of a public key certificate in a signature value of a metadata producer with a metadata access control descriptor embedded in the content.

Further, according to the embodiment of the present invention, a proper hierarchical structure is provided to information of an owner of a certificate, and a metadata access control descriptor corresponding to the hierarchical structure (the metadata access control descriptor 1 or 2 in FIG. 10 ) is defined. Therefore, it is possible to achieve an access control to content from metadata according to an organization attribute of a producer of the metadata.

In the above embodiment, as shown in FIG. 8 , content and license information (Kc transmission ECM/EMM) including an identifier (metadata access control descriptor) are multiplexed and transmitted by the multiplexing means 63 . However, the content and the license information are not necessarily required to be transmitted together. For example, license information (Kc transmission ECM/EMM) in which an identifier (metadata access control descriptor) is embedded may be transmitted after only content is transmitted.