JP2022134647A - transmitter and receiver - Google Patents

Abstract

To allow even a receiver without communication function to decrypt content encrypted by the CENC method in a digital broadcasting system based on the ARIB standard.SOLUTION: A transmitter 100 for a digital broadcasting system includes: an ECM generation unit 122 that generates an ECM including a set of a content key Kc for encrypting content and key identification information KID indicating the content key Kc; and a multiplexing unit 140 that multiplexes and transmits encrypted content which is content encrypted with the content key Kc and to which the key identification information KID is assigned and the ECM generated by the ECM generation unit 122.SELECTED DRAWING: Figure 4

Description

The present invention relates to transmitters and receivers for digital broadcasting systems.

In conventional digital broadcasting, a conditional access system in which only subscribers are allowed to receive broadcasts in pay broadcasting, and a content protection system for free broadcasting are used. In these access control schemes, broadcast content is encrypted. As a mechanism for safely distributing encryption keys for decrypting encrypted content, a related information subsystem (triple key system) that distributes encryption keys using key-related information is used ( See Non-Patent Documents 1 and 2).

In the related information subsystem, the encrypted encryption key is transmitted as key related information common to the receiving apparatus called ECM (Entitlement Control Message). The format of this ECM and the encryption method for the encryption key are determined for each access control method, for example, CAS (Conditional Access System) for pay broadcasting and RMP (Rights Management and Protection) for free broadcasting. is used.

On the other hand, DRM (Digital Rights Management) known as communication content protection technology includes Microsoft's PlayReady, Google's Widevine, Apple's Fairplay, and the like. As a content encryption method for realizing support for various client terminals that support these different DRM technologies, a method called CENC (Common Encryption) of MPEG (Moving Picture Experts Group) is known (non-patent Reference 3).

This CENC system is an international standard technology that enables the same encrypted content to be decrypted in the same manner by different DRMs and key management systems. Specifically, by adding multiple DRM support information to the header of the encrypted content, any client terminal that supports any DRM can acquire the corresponding license including the content encryption key from the license server. , it is possible to decrypt and play encrypted content.

U.S. Patent Application Publication No. 2018/0373847

ARIB STD-B25 "Access control method for digital broadcasting" ARIB STD-B61 "Access control method for digital broadcasting (2nd generation) and CAS program download method" Volume 1 "Access control method (2nd generation)" ISO/IEC 23001-07 "Information technology -MPEG systems technologies- Part7: Common encryption in ISO base media file format files"

In the future, not only television receivers equipped with tuners but also various client terminals such as smartphones and tablet terminals will be expected to transmit content via broadcasting. In this case, since content protection technologies supported by client terminals differ, it is considered effective to broadcast content encrypted by the CENC scheme, which realizes compatibility with multiple DRMs.

However, the CENC method is based on the premise that a client terminal that receives encrypted content acquires a license from a license server via communication. I have a problem that I can't.

In order to address such issues, Patent Document 1 proposes a technique related to a DRM license acquisition method in a receiver conforming to the ATSC 3.0 standard, but a license acquisition method for a broadcasting system conforming to the ARIB standard has not necessarily been established. It has not been.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a transmitting device and a receiving device in a digital broadcasting system based on the ARIB standard, which enables even a receiving device having no communication function to decrypt content encrypted by the CENC method. and

A transmitting device according to a first aspect is a transmitting device for a digital broadcasting system. A transmission device includes an ECM generation unit that generates an ECM including a set of an encryption key for encrypting content and key identification information indicating the encryption key, and content encrypted with the encryption key, A multiplexing unit that multiplexes the encrypted content to which the key identification information is attached and the ECM generated by the ECM generation unit and transmits the multiplexed content.

A receiving device according to a second aspect is a receiving device for a digital broadcasting system. A receiving device receives encrypted content that is encrypted with an encryption key and to which key identification information indicating the encryption key is added, and an ECM that includes a set of the encryption key and the key identification information. a separation unit that separates from the received stream; a key management unit that acquires the set from the ECM and holds the acquired set; A key identification unit that identifies and obtains from the key management unit, and a content decryption unit that decrypts the encrypted content using the encryption key obtained by the key identification unit.

According to the present invention, in a digital broadcasting system based on the ARIB standard, it is possible to provide a transmitting device and a receiving device that enable even a receiving device that does not have a communication function to decrypt content encrypted by the CENC system.

1 is a diagram showing the configuration of a digital broadcasting system according to an embodiment; FIG. FIG. 4 is a diagram showing the configuration of CENC-encrypted content according to the embodiment; It is a figure which shows an example of the sequence in the digital broadcasting system which concerns on embodiment. 1 is a diagram showing the configuration of a transmission device according to an embodiment; FIG. It is a figure which shows the 1st structural example of ECM which concerns on embodiment. It is a figure which shows the 2nd structural example of ECM which concerns on embodiment. It is a figure which shows the structure of the receiver which concerns on embodiment. It is a figure which shows an example of the information managed by the key management part which concerns on embodiment. It is a figure which shows the operation|movement flow of the receiver which concerns on embodiment.

A transmitting device and a receiving device according to embodiments will be described with reference to the drawings.

(Digital broadcasting system)
First, a digital broadcasting system according to this embodiment will be described. FIG. 1 is a diagram showing the configuration of a digital broadcasting system 1 according to this embodiment.

As shown in FIG. 1, the digital broadcasting system 1 is a broadcasting system based on the ARIB standard, and has a transmitting device 100, a receiving device 200, and a license server 300. FIG.

The transmission device 100 is a device that transmits encrypted content. A transmitting device 100 is provided, for example, in a broadcasting station. In the present embodiment, the transmitting device 100 transmits a stream including content encrypted by the CENC method (hereinafter referred to as "CENC-encrypted content").

The receiving device 200 is a device that receives encrypted content. The receiving device 200 is, for example, a television receiving device (television tuner), a PC (Personal Computer), a smart phone, a tablet terminal, or the like. In FIG. 1, as the receiving device 200, receiving devices 200a to 200c are illustrated. The receiving devices 200a and 200b have a communication function and are connected to the communication network 10 by wire or wirelessly. On the other hand, the receiving device 200c does not have a communication function and does not have a connection with the communication network 10. FIG.

Communication network 10 includes the Internet. The communication network 10 may include a LAN (Local Area Network) or a cellular communication network. The LAN may be a wired LAN or a wireless LAN.

The license server 300 is a device that is connected to the communication network 10 and issues and manages a key (hereinafter referred to as an "encryption key") for decrypting CENC-encrypted content. Although one license server 300 is illustrated in FIG. 1, a different license server 300 may be provided for each DRM system (business entity). In the CENC system, such an encryption key is called a content key Kc.

FIG. 2 is a diagram showing the configuration of CENC-encrypted content according to this embodiment.

As shown in FIG. 2, CENC encrypted content has a header portion and a payload portion. The header part contains additional information (meta-information) in the CENC-encrypted content. The payload portion includes encrypted content data obtained by encrypting content such as video and audio with the content key Kc.

In this embodiment, the header portion of the CENC-encrypted content includes key identification information KID, which is information indicating the content key Kc of the content and is defined by the CENC scheme, and the system ID of the DRM system. The system ID is a unique identifier that identifies the DRM system (scheme).

In FIG. 1, the receiving device 200a receives CENC-encrypted content from the transmitting device 100 via the communication network . The receiving device 200a acquires the key identification information KID and the system ID from the header portion of the received CENC-encrypted content, transmits the key identification information KID to the license server 300 corresponding to this system ID, and obtains the key identification information KID. A content key Kc corresponding to KID can be obtained from the license server 300 .

The receiving device 200 b receives the CENC-encrypted content from the transmitting device 100 via the broadcast transmission line 20 . The broadcast transmission line 20 is a transmission line for terrestrial broadcasting, satellite broadcasting, cable broadcasting, or the like. Since the receiving device 200b has a communication function, it can acquire the content key Kc from the license server 300 in the same manner as the receiving device 200a.

The receiving device 200 c receives the CENC-encrypted content from the transmitting device 100 via the broadcast transmission line 20 . Since the receiving device 200 c does not have a communication function, it cannot acquire the content key Kc from the license server 300 .

In this way, in order to transmit content via broadcasting to various receiving devices 200, it is effective to transmit content encrypted by the CENC scheme. The content key Kc cannot be obtained from the license server 300, and the CENC-encrypted content cannot be decrypted.

Therefore, in the present embodiment, the transmission device 100 multiplexes an ECM including a set of the content key Kc and the key identification information KID indicating the content key Kc with the CENC-encrypted content and transmits the multiplexed ECM. ECM is a type of key-related information defined by the ARIB standard. The multiplexing method may be MMT (MPEG Media Transport) or MPEG2-TS (Transport Stream).

Thereby, the receiving device 200 can acquire the content key Kc corresponding to the key identification information KID attached to the received CENC-encrypted content from the ECM. Therefore, even the receiving device 200 that does not have a communication function can acquire the content key Kc and decrypt the CENC-encrypted content. Therefore, in the digital broadcasting system 1 based on the ARIB standard, even the receiver 200c having no communication function can decrypt the contents encrypted by the CENC system.

FIG. 3 is a diagram showing an example of a sequence in the digital broadcasting system 1 according to this embodiment.

As shown in FIG. 3, the transmitting device 100 transmits a control message to the receiving device 200 in step S1. The transmitting device 100 may periodically transmit control messages. The control message includes a package configuration description table for the receiving device 200 to receive key-related information.

In step S<b>2 , the transmitting device 100 transmits key-related information to the receiving device 200 . The transmitting device 100 may periodically transmit key-related information. Key-related information includes EMM (Entitlement. Management Message) and ECM. ECM includes a set of content key Kc and key identification information KID.

In step S<b>3 , transmitting device 100 transmits the CENC-encrypted content to receiving device 200 . CENC-encrypted content is content encrypted with a content key Kc. Key identification information KID of this content key Kc is assigned to CENC-encrypted content. The receiving device 200 acquires the content key Kc corresponding to the key identification information KID assigned to the CENC-encrypted content from the ECM received in step S2, and decrypts the CENC-encrypted content using the acquired content key Kc. .

(Transmitter)
Next, the transmission device 100 according to this embodiment will be described. FIG. 4 is a diagram showing the configuration of the transmission device 100 according to this embodiment.

As shown in FIG. 4 , transmitting device 100 has encrypted content generator 110 , key-related information generator 120 , control message generator 130 , and multiplexer 140 .

The encrypted content generation unit 110 encrypts video/audio file content in ISO-BMFF (ISO-Base Media File Format) format using a content key Kc to generate CENC-encrypted content. The configuration of the CENC-encrypted content is as per the standard specification of Non-Patent Document 3. Meta information indicating encryption parameters (system ID indicating a DRM system, KID indicating key identification information, etc.) is at least contained in the Content Protection Descriptor of the manifest MPD (Media Presentation description) of MPEG-DASH or in the moov/moof box. In addition to being described in the pssh box, it is described in the tenc box of the moov box and the sgpd box of the moof box.

The key-related information generation unit 120 generates key-related information such as ECM and EMM, and generates a section that wraps them. The key-related information generator 120 has an EMM generator 121 and an ECM generator 122 .

The EMM generation unit 121 generates an EMM that is key-related information for each receiving device 200 or for each type of receiving device 200 (for each manufacturer, etc.). In the case of individual receiving devices 200, the key-related information (work key Kw) is encrypted using a different key (master key Km) for each receiving device 200 and sent. In the case of each type of receiving device 200, the key-related information (work key Kw) is encrypted using a different key (device key Kd) for each type of receiving device 200 and sent.

The ECM generator 122 generates ECM, which is key-related information common to the receiving device 200 . The ECM generation unit 122 encrypts an ECM containing at least a set (correspondence relationship) of the content key Kc of the CENC-encrypted content and the key identification information KID with the work key Kw and sends the ECM. A configuration example of the ECM will be described later.

The control message generator 130 generates various control messages. The control message generation unit 130 creates a package configuration description table to be transmitted in the control message, more specifically, a table that indicates the information of the contents that make up the package (program) and the packet of the key-related information related to the encryption. Generate. For example, in the case of MMT, the package configuration and ECM packet ID are specified in the MMT package table (MPT), and the EMM packet ID is specified in the CA table (CAT). In the case of MPEG2-TS, program stream information and ECM packet ID are specified in PMT, and EMM packet ID is specified in CAT.

The multiplexer 140 combines the CENC-encrypted content generated by the encrypted content generator 110, the key-related information (EMM and ECM) generated by the key-related information generator 120, and the control message generated by the control message generator 130. The received control message is multiplexed by MMT or MPEG2-TS, and a stream is output.

(First configuration example of ECM)
Next, a first configuration example of the ECM according to this embodiment will be described. FIG. 5 is a diagram showing a first configuration example of the ECM according to this embodiment.

In the configuration example shown in FIG. 5, the ECM has a protocol number, entity identification information, work key identification information, key identification information KID, content key Kc, expiration date information, and tampering detection.

The protocol number is information that identifies the ECM format and includes encryption/decryption algorithm parameters. If the ECM includes a set of key identification information KID and content key Kc, the protocol number may be set to a special value indicating that it includes a set of key identification information KID and content key Kc.

The business entity identification information is information indicating the business entity that issues the content key Kc. Note that different entities may use the same value of key identification KID. Therefore, by associating the business entity identification information with the key identification information KID in the ECM, it becomes easier for the receiving device 200 to identify the correct content key Kc. Specifically, even if a content key Kc linked to duplicate key identification information KID is issued by a different entity, the receiving device 200 side determines the correct content key Kc based on the entity identification information and the key identification information KID. It becomes possible to identify the content key Kc.

The work key identification information is information indicating the work key Kw used for decrypting the ECM.

The key identification information KID is information indicating the content key Kc. The key identification information KID is stored in the ECM in association with the content key Kc.

The validity period information is information indicating the validity period of the set of the key identification information KID and the content key Kc included in this ECM. The expiration date may be specified by an absolute time described in NTP (Network Time Protocol) time stamp format or the like, or may be specified by a relative time such as a timer value counted down from the time of ECM reception. By transmitting such validity period information, it becomes possible to set a valid period for the set of the content key Kc and the key identification information KID.

Tampering detection is information for detecting ECM tampering.

Among these pieces of information, the key identification information KID, content key Kc, and expiration date information are encrypted with the work key Kw.

(Second configuration example of ECM)
Next, a second configuration example of the ECM according to this embodiment will be described. FIG. 6 is a diagram showing a second configuration example of the ECM according to this embodiment.

In the configuration example shown in FIG. 6, a plurality (three sets) of sets of key identification information KID, content key Kc, and expiration date information are included in the same ECM. Thereby, a plurality of content keys Kc can be collectively transmitted.

For example, when the transmitting device 100 frequently switches the content key Kc used for encrypting the content, the receiving device 200 stores a plurality of content keys Kc in advance so that when the content key Kc is switched, the content key Kc is changed. Therefore, it is possible to quickly decode the content on the receiving device 200 side.

(receiving device)
Next, the receiving device 200 according to this embodiment will be described. FIG. 7 is a diagram showing the configuration of the receiving device 200 according to this embodiment.

As shown in FIG. 7, the receiving device 200 includes a separation unit 210, a key-related information identification unit 220, a key-related information processing unit 230, a key management unit 240, a key identification unit 250, and a content decryption unit 260. , a content reproduction unit 270 and a reproduction control unit 280 .

Separator 210 separates the control message, key-related information (EMM and ECM), and CENC-encrypted content from the received stream. Separating section 210 outputs a control message (package configuration description table) to key-related information identifying section 220 , outputs key-related information to key-related information processing section 230 , and outputs CENC-encrypted content to key identifying section 250 . .

The key-related information identifying unit 220 identifies packet IDs of the ECM and EMM from the package configuration description table, and outputs the identified packet IDs to the key-related information processing unit 230 .

The key-related information processing unit 230 extracts the ECM and EMM from the key-related information based on the packet ID specified by the key-related information specifying unit 220, and processes the key-related information. The key-related information processing section 230 has an EMM processing section 231 and an ECM processing section 232 .

The EMM processing unit 231 uses the pre-embedded keys (master key Km/device key Kd) to decrypt the encrypted part of the EMM, extracts the work key Kw, and supplies the work key Kw to the ECM processing unit 232. Output.

The ECM processing unit 232 uses the work key Kw obtained from the EMM processing unit 231 to decrypt the encrypted part of the ECM and obtains a set of the key identification information KID and the content key Kc. At that time, the ECM processing unit 232 also acquires expiration date information, entity identification information, and the like, and outputs them to the key management unit 240 .

The key management unit 240 holds a set of key identification information KID and content key Kc. FIG. 8 is a diagram showing an example of information managed by the key management unit 240. As shown in FIG.

As shown in FIG. 8, the key management unit 240 associates business entity identification information indicating a code that identifies the business entity issuing the key, key identification information KID, content key Kc, and expiration date information. attach and hold. The key management unit 240 deletes or invalidates information (key identification information KID and content key Kc) whose validity period indicated by the validity period information has passed. Disabling means not deleting the information, but making it unusable.

With the management method shown in FIG. 8, the key management unit 240 can simultaneously hold a plurality of sets (correspondence between the key identification information KID and the content key Kc). Since some sets can be deleted or invalidated by using For example, depending on the expiration date setting, it is possible to keep a specific set valid for a long period of time. The protected content can be viewed without changing the content key Kc.

Returning to FIG. 7, the key identification unit 250 refers to the information described in the tenc box included in the moov box that stores the meta information of the CENC-encrypted content or the sgpd box included in the moof box to obtain the key identification information. KID is determined, and the content key Kc corresponding to this key identification information KID is specified and acquired from the key management unit 240 . At that time, by combining the key identification information KID and the entity identification information and inquiring the key management unit 240, even if the same key identification information KID is used by different entities, the unique content key Kc can be specified. Here, the key identification unit 250 uses the business entity identification information (business entity entity), and inquires of the key management unit 240 by combining the identified business entity identification information and key identification information KID. Note that, when business entity identification information is attached to the CENC-encrypted content, the key identification unit 250 may make an inquiry to the key management unit 240 using this business entity identification information.

Content decryption section 260 decrypts the CENC-encrypted content using content key Kc identified by key identification section 250 and outputs the decrypted content to content reproduction section 270 .

Content reproduction section 270 reproduces the content decrypted by content decryption section 260 .

The reproduction control unit 280 controls reproduction of CENC-encrypted content. This playback control may be control by user operation via a user interface, or may be control by an application programmed to perform automatic playback.

FIG. 9 is a diagram showing an operation flow of the receiving device 200 according to this embodiment.

As shown in FIG. 9, in step S11, the separation unit 210 and the key-related information specifying unit 220 refer to the package configuration description table to extract key-related information (EMM and ECM), and use the extracted key-related information as a key. Output to related information processing section 230 .

In step S12, the key-related information processing section 230 processes the key-related information. Here, the ECM processing unit 232 extracts a set of the key identification information KID and the content key Kc from the ECM.

In step S13, the key management section 240 stores a set of the key identification information KID and the content key Kc. The key management unit 240 may also store business entity identification information and expiration date information.

In step S<b>14 , the key identification unit 250 acquires the CENC-encrypted content based on the reproduction trigger from the reproduction control unit 280 .

In step S15, the key identification unit 250 identifies the key identification information KID by referring to the meta information included in the header portion of the CENC-encrypted content.

In step S16, the key identification unit 250 makes an inquiry to the key management unit 240 based on the key identification information KID, and acquires the content key Kc.

In step S17, the content decryption section 260 decrypts the CENC-encrypted content using the obtained content key Kc.

In step S18, the content reproduction unit 270 reproduces the decrypted content.

(Other embodiments)
In the above-described embodiment, an example of transmitting content encrypted by the CENC method (CENC-encrypted content) from the transmitting device 100 to the receiving device 200 has been described. However, any method may be used as long as it transmits encrypted content to which key identification information is added, and is not limited to the CENC method.

In the above-described embodiment, the receiving device 200 is mainly assumed to be the receiving device 200c that does not have a communication function. However, the configuration and operation according to the above-described embodiments may also be applied to the receivers 200a and 200b having communication functions.

It may be provided as a program that causes a computer to execute each process performed by the transmission device 100 . Alternatively, the program may be provided as a program that causes a computer to execute each process performed by the receiving device 200 . The program may be recorded on a computer readable medium. A computer readable medium allows the installation of the program on the computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be, for example, a recording medium such as CD-ROM or DVD-ROM.

A circuit that executes each process performed by the transmission device 100 may be integrated, and the transmission device 100 may be configured by a semiconductor integrated circuit (chipset, SoC). A circuit that executes each process performed by the receiving device 200 may be integrated, and the receiving device 200 may be configured by a semiconductor integrated circuit (chipset, SoC).

Although the embodiments have been described in detail with reference to the drawings, the specific configuration is not limited to the above, and various design changes can be made without departing from the spirit of the invention.

1: Digital broadcasting system 10: Communication network 20: Broadcast transmission path 100: Transmitter 110: Encrypted content generator 120: Key related information generator 121: EMM generator 122: ECM generator 130: Control message generator 140: Multiplexing unit 200 : Receiving device 210 : Separating unit 220 : Key-related information specifying unit 230 : Key-related information processing unit 231 : EMM processing unit 232 : ECM processing unit 240 : Key management unit 250 : Key specifying unit 260 : Content decoding unit 270: Content playback unit 280: Playback control unit 300: License server

Claims (10)

A transmitting device for a digital broadcasting system,
an ECM generator that generates an ECM including a set of an encryption key for encrypting content and key identification information indicating the encryption key;
a multiplexing unit that multiplexes and outputs encrypted content encrypted with the encryption key and to which the key identification information is added and the ECM generated by the ECM generation unit;
A transmitting device comprising: The encrypted content is encrypted by the CENC method,
The encryption key is a content key Kc defined by the CENC system,
2. The transmitting apparatus according to claim 1, wherein said key identification information is key identification information KID defined by said CENC system. 3. The transmitting apparatus according to claim 1, wherein the ECM generator generates the ECM, the ECM further including expiration date information indicating the expiration date of the encryption key in the set. 4. The transmitting apparatus according to any one of claims 1 to 3, wherein said ECM generator generates said ECM including a plurality of said sets. 5. The transmitting apparatus according to any one of claims 1 to 4, wherein said ECM generation unit generates said ECM including business entity identification information indicating a business entity that issues said encryption key. A receiving device for a digital broadcasting system,
Separating encrypted content, which is encrypted with an encryption key and to which key identification information indicating the encryption key is added, and ECM including a set of the encryption key and the key identification information from the received stream. a separation unit that
a key management unit that acquires the set from the ECM and holds the acquired set;
a key identification unit that identifies and acquires the encryption key corresponding to the key identification information assigned to the encrypted content from the key management unit;
a content decryption unit that decrypts the encrypted content using the encryption key acquired by the key identification unit;
A receiving device comprising: The encrypted content is encrypted by the CENC method,
The encryption key is a content key Kc defined by the CENC system,
7. The receiving apparatus according to claim 6, wherein said key identification information is key identification information KID defined by said CENC system. the set included in the ECM further includes expiration date information indicating the expiration date of the encryption key;
8. The receiving apparatus according to claim 6, wherein said key management unit deletes or invalidates said set including said encryption key whose expiration date has passed. 9. The receiving apparatus according to any one of claims 6 to 8, wherein said ECM includes a plurality of said sets. The ECM further includes business entity identification information indicating the business entity that issues the encryption key,
The key management unit manages the set in association with the entity identification information,
The key identification unit identifies the entity from which the encryption key is to be obtained, and the key identification information corresponding to the entity identification information of the identified entity and the key identification information added to the encrypted content. 10. The receiving apparatus according to any one of claims 6 to 9, wherein an encryption key is obtained from said key management unit.

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