KR102286303B1 - Key Rotation for DRM Systems in DASH base Media Service - Google Patents

Abstract

The present invention relates to a key rotation method for a DRM system in a DASH-based media content service.
According to an aspect of this embodiment, the DASH encoder generates a plurality of media decryption keys and provides a key list including the generated media decryption keys to the content protection manager. In the key list, each media decryption key is identified by a key identifier (KID). The content protection manager transmits the key list received from the DASH encoder to the license server. The license server generates a plurality of ECLs based on the key list, and transmits the ECL list including the generated ECLs to the content protection manager. In the ECL list, each ECL is identified by a key identifier and includes an encrypted media decryption key and a key identifier. The content protection manager creates a pssh box in which the ECL list is inserted in a data field, and delivers the generated pssh box to the DASH encoder. The DASH encoder includes the pssh box in the DASH MPD or media segment and delivers it to the client terminal.

Description

Key Rotation for DRM Systems in DASH base Media Service

The present invention relates to a key rotation for a DRM (Digital Rights Management) system in a DASH (Dynamic adaptive streaming over HTTP) based media service.

The content described in this section merely provides background information for the present embodiment and does not constitute the prior art.

ECL (Entitlement Control License) is one of the methods for content protection when providing DASH-based media services. DASH (Dynamic adaptive streaming over HTTP) can protect media content based on the MPEG CENC standard, and in this case, media content is basically encrypted with an encryption key. There are several factors that differentiate the strength of content protection, and one of them is to periodically change the encryption key. Periodically changing the encryption key is called "key rotation." ECL is a license used in the key hierarchy method, which is one of the methods of changing the encryption key for key rotation.

The standards presented so far are "ECL and EML (Entitlement Management License) can be used if you want to use the key hierarchy method when encrypting DASH-based media with the key rotation method, and the ECL includes an encrypted media decryption key, EML is only described to the extent of "must include a decryption key necessary to decrypt the encrypted media decryption key", but does not specify the detailed operation of ECL and EML. In the case of EML, there is no problem even if it is operated using the content security provider's own method, but in the case of ECL, since it is data that is included in the media and transmitted through the media and transmission channel, a clearer standardized protocol is required.

The main object of the present invention is to provide an ECL operation method that satisfies these requirements.

According to one aspect of the present invention, there is provided a method for managing secure distribution of media content in a system for a DASH-based media service. The method includes, by the DASH encoder, generating a plurality of media decryption keys, and providing a key list including the generated media decryption keys to the content protection manager. In the key list, each media decryption key is identified by a key identifier (KID). The method may include transmitting, by the content protection manager, a key list received from the DASH encoder to a license server; and generating, by the license server, a plurality of ECLs based on the key list, and transmitting the ECL list including the generated ECLs to the content protection manager. In the ECL list, each ECL is identified by a key identifier and includes an encrypted media decryption key and a key identifier. The method includes: the content protection manager generating a pssh box in which the ECL list is inserted in a data field, and transmitting the generated pssh box to the DASH encoder; and transmitting, by the DASH encoder, the pssh box to a DASH Media Presentation Description (MPD) or media segment to be transmitted to the client terminal.

Embodiments of the method may further include one or more of the following features.

In some embodiments, the method includes: parsing, by a DASH decoder, a DASH stream, and delivering the pssh box to a DRM client; and decrypting, by the DRM client, a key list from a plurality of ECLs included in the pssh box, using a decryption key included in the EML obtained in advance. Here, the DASH decoder and the DRM client are included in the client terminal.

In some embodiments, the method comprises: storing, by the DRM client, a decrypted key list in a storage in the client terminal; transmitting, by the DASH decoder, a key identifier of a media decryption key to be used in a current key change period to the DRM client; a process in which the DRM client searches for a media decryption key corresponding to the key identifier received from the DASH decoder in the storage, and transmits the retrieved media decryption key to the DASH decoder; and decoding, by the DASH decoder, the media segments received in the current key change period using the media decryption key received from the DRM client.

According to another aspect of the present invention, there is provided a computerized device operating as a content protection manager managing secure distribution of media in a system for a DASH-based media content service, comprising: a memory for storing computer program instructions; one or more processors; input/output interface circuit; and one or more data buses interconnecting the memory, the processor, and the input/output interface circuit, wherein the processor executes the computer program instructions to cause the computerized device to perform the following process. : A process of delivering a key list including media decryption keys from a DASH encoder to a license server, wherein each media decryption key in the key list is identified by a Key Identifier (KID); receiving, from the license server, an ECL list generated based on the key list, wherein each ECL in the ECL list is identified by a key identifier and includes an encrypted media decryption key and a key identifier; A process of generating a pssh box in which the ECL list is inserted in a data field, and transmitting the generated pssh box to the DASH encoder. Here, the pssh box is included in the DASH MPD or media segment by the DASH encoder and delivered to the client terminal.

According to another aspect of the present invention, a system for a DASH-based media content service includes one or more server computers connected to a client terminal through a content delivery network and including a DASH encoder, a content protection manager, and a license server. The DASH encoder generates a key list including a plurality of media decryption keys identified by a key identifier (KID), and includes a pssh box received from the license server in a DASH MPD (Media Presentation Description) or media segment. configured to deliver to the client terminal. In the key list, each media decryption key is identified by a key identifier (KID). The license server operates to generate a plurality of ECLs based on the key list and to transmit the ECL list including the generated ECLs to the content protection manager. Each ECL contains a corresponding encrypted media decryption key and key identifier. The content protection manager receives the key list from the DASH encoder and delivers it to the license server, generates a pssh box in which the ECL list received from the license server is inserted, and delivers the generated pssh box to the DASH encoder. It works. Here, the ECL list is included in the Data field of pssh.

As described above, according to the present invention, an ECL operation protocol is provided when providing a key rotation function in an ECL-based key hierarchy method in a DASH-based media service.

In addition, according to the present invention, since continuously changing media keys are transmitted in-band, real-time license acquisition is possible, and repeated client authentication or authorization is not required. Accordingly, continuous content reproduction is possible without interruption.

1 is a diagram illustrating components constituting a DRM system and a communication flow.
2 is a diagram illustrating a method of providing information on ECL-based current and future keys to a pssh box according to an embodiment of the present invention.
3 is a flowchart illustrating a content transmission and decryption method using a key change according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same components are given the same reference numerals as much as possible even though they are indicated on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

Throughout the specification, when a part 'includes' or 'includes' a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated. . Also, as used herein, the term 'server' refers to a general general purpose or special purpose computer system, which usually includes an interconnection such as memory, input/output circuitry, and one or more data buses connecting these components. Contains instruction processing logic with Accordingly, the techniques disclosed herein may be implemented in software executed by one or more computer systems. Similarly, a client terminal is a computerized device including the above components and software executing, which is a computerized device capable of receiving content from a network, decoding the received content, and rendering it on a display or similar output devices. am.

1 is a diagram illustrating a content delivery system according to an embodiment of the present invention.

The content delivery system 100 includes a DASH encoder ( 10 ), a content protection manager ( CP managerl 12 ), a license server ( 14 ), and a client terminal ( 20 ). The DASH encoder 10 , the content protection manager 12 , and the license server 14 functionally distinguish a DRM system that is a part of a service platform that provides a media content service (eg, an over-the-top (OTT) service). They are logical objects. Accordingly, one or more physical objects (ie, a server computer system) may perform roles performed by a plurality of logical objects. For example, in some embodiments, the content protection manager 12 and the license server 14 may be included on the same physical server.

The DASH encoder 10 generates a media stream to be delivered to the client terminal 20 . The DASH encoder 10 encrypts content using an encryption technique standardized in accordance with a content format such as an ISO-based media file format [ISO/EC 14496-12]. The DASH encoder 10 implements a key rotation function with duration. That is, the DASH encoder 10 encrypts the media segments using a different encryption key for each key change period.

The content protection manager 12 cooperates with the DASH encoder 10 and the license server 14 to manage distribution of a content decryption key used for media stream protection.

A license server (Licence server) 14 cooperates with the content protection manager 12 to generate licenses to be delivered to the authorized client terminal 20 . Licenses include an Entitlement Management License (EML) and an Entitlement Control License (ECL). The ECL includes information on media decryption keys used by the client terminal 20 to decrypt encrypted content, and the EML includes key information used to extract a media decryption key from the ECL. A description of the transfer of licenses will be described later with reference to FIGS. 2 to 3 .

The content delivery system 100 may further include an authentication server (not shown) to implement an authentication/authorization function. The authentication server cooperates with the service protection manager 12 to perform user authentication and confirmation of subscriber information. When the service is accessed by the user, the authentication server may perform authentication and authorization by verifying the user ID and password stored in the subscriber management system (not shown) of the service operator. The authentication server transmits this result to the service protection manager 12, and DASH stream generation including license processing begins .

The client device 20 receives a license and a DASH stream based on a user's play request, and decrypts and plays the DASH stream using a media decryption key included in the license. The client terminal 20 includes a DASH decoder 21 and a DRM client 22 . In some embodiments, the DRM client 22 may have a playback function (ie, decoder function) embedded in the client terminal 20 for decoding and display of content. The client terminal 20 includes a set-top box or a non-set-top box (eg, a smart phone, a tablet PC, a notebook computer, etc.).

The content delivery system 100 supports a "key rotation" function that updates keys over time. The media decryption key is changed at set time intervals for the security of content protection. Key change is mainly used to change entitlements while streaming content. The present invention uses a so-called 'Key hierarchy' method using ECL and EML when encrypting DASH-based media using a key rotation method.

2 is a diagram illustrating a method of providing information on ECL-based current and future keys to a pssh box according to an embodiment of the present invention.

MPEG CENC (Common Encryption; ISO/IEC 23001-7) standard is an encryption method (Encryption Method) for ISO base media file format (ISOBMFF), an encryption key mapping method, a method for displaying encryption metadata (Encryption Metadata) It is a common encryption standard that includes This standard enables different content protection systems to encrypt/decrypt ISOBMFF with a common method rather than their own encryption method. Allows you to focus on managing access rights (Rights, Licenses, etc.).

Under the MPEG/3GP DASH protocol media segments or initialization segments can be used to convey new media keys that change within a track. The initialization segments include one or more Protection System Specific Header boxes (pssh boxes) under the Movie box (moov box) defined by the MPEG CENC standard. Media segments may include pssh boxes under Movie Fragment boxes (moof boxes). Also, the pssh box may be included in a Media Presentation Description (MPD).

The pssh boxes transmit information about new keys or licenses, and the client terminal obtains information from pssh boxes in the initialization segment or media segment to obtain media decryption keys.

As shown in FIG. 2 , the pssh box includes at least two KID/ECL pairs for current and future content keys, and includes the same KID/ECL pair value for each key change period. The reason that at least two are needed is to secure the necessary KID/ECL before the next key rotation occurs so that the service is not interrupted or delayed. In general, it is necessary to include more than two so that the so-called "client storm" phenomenon in which client terminals request a new key from the license server at once at the boundary of key change does not occur.

3 is a flowchart illustrating a content transmission and decryption method using a key change according to an embodiment of the present invention.

The 'DRM system X' shown in FIG. 3 is an example of one of the dedicated DRM systems, and the license server and the DRM client are exclusive to the DRM system X.

The DASH encoder generates a KID/KEY pair list in which the KID and KEY, which is the media decryption key, are paired (S310). Here, KID means a key identifier assigned to KEY. There should be at least two KID/KEY pairs. The KID/KEY pair configuration can be configured differently for each DRM solution. The generated pairs are It is transmitted to the content protection manager (S311) The media decryption key is used by the DASH decoder to decrypt the media segment.

The content protection manager delivers the KID/KEY pair list received from the DASH encoder to the license server (S312).

The license server generates ECLs based on the KID/KEY pair list (S313). Each ECL contains an encrypted KID/KEY pair. Thereafter, the license server transmits the ECL list including the generated ECLs to the content protection manager (S314). In the ECL list, each ECL is identified by a KID. In this case, the KID/KEY encryption method and the ECL configuration may be different for each DRM system.

The content protection manager creates a pssh box based on the KID/ECL pairs (S315). At this time, KID/ECL pairs must be included in the Data field of pssh, not pssh itself. The generated pssh box is delivered to the DASH encoder (S317).

The DASH encoder streams encrypted content to the DASH decoder according to the MPEG DASH standard by using the KEY used in the current key change section from the generated KID/KEY list. At this time, the DASH encoder includes the pssh box received from the content protection manager in the MPD or media segment and delivers it to the client terminal (S317).

The DASH decoder parses the received DASH stream and extracts the pssh box. Thereafter, the DASH decoder delivers the pssh box to the DRM client (S318).

The DRM client decrypts the KID/KEY pairs from the received ECLs and stores them in a secure database (S319 to S320). The decryption key used to decrypt the KID/KEY pair is obtained from EML. An EML configuration and processing method may be adopted in an appropriate manner for each DRM solution, which is outside the scope of the present invention.

When the DRM client receives the KID value from the DASH decoder, the DRM client retrieves the KEY corresponding to the KID from the KID/KEY pair stored in the storage and delivers the retrieved KEY to the DASH decoder (S321 to S323).

The DASH decoder decodes the DASH media stream using the received KEY (S324).

As described above, since continuously changing media keys are delivered together with the MPD or media segment, real-time license acquisition is possible, and repeated client authentication or authorization is not required. Accordingly, continuous content reproduction is possible without interruption.

3, the KID/KEY list generated by the DASH encoder has been described as being delivered to the content protection manager and the license server, but in another embodiment, the content protection manager or the license server generates the KID/KEY list can be configured to do so. For example, the content protection manager may generate a KID/KEY list and deliver it to the DASH encoder and the license server.

In the above embodiment, MPEG/3GP Dynamic Adaptive Streaming over HTTP (DASH) has been exemplarily described as a segment-based content distribution protocol, but the present invention also includes other segment-based protocols (eg, HTTP live Streaming, Silverlight Smooth Streaming, etc.). It is obvious that the proposed key exchange method can be applied.

The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Accordingly, the above-described embodiments are for explanation rather than limiting the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (5)

A method for managing secure distribution of media content in a system for a DASH-based media service, the method comprising:
A process in which the DASH encoder generates a plurality of media decryption keys and provides a key list including the generated media decryption keys to the content protection manager, wherein each media decryption key in the key list is identified by a Key Identifier (KID) identified;
transmitting, by the content protection manager, the key list received from the DASH encoder to a license server;
A process in which the license server generates a plurality of Entitlement Control Licenses (ECLs) based on the key list and transmits the ECL list including the generated ECLs to the content protection manager. In the ECL list, each ECL is identified by a key identifier. identified and containing an encrypted media decryption key and a key identifier;
generating, by the content protection manager, a pssh box in which the ECL list is inserted in a data field, and transmitting the generated pssh box to the DASH encoder;
a process in which the DASH encoder includes the pssh box in a DASH MPD (Media Presentation Description) or a media segment and transmits it to the client terminal;
a process in which the DASH decoder parses the DASH stream and delivers the pssh box to the DRM client, wherein the DASH decoder and the DRM client are included in the client terminal; and
A process in which the DRM client decrypts the key list by using a decryption key included in an EML (Entitlement Management License) obtained in advance from a plurality of ECLs included in the pssh box
A method for managing secure distribution of media content, comprising: According to claim 1,
storing, by the DRM client, a decrypted key list in a storage in the client terminal;
transmitting, by the DASH decoder, a key identifier of a media decryption key to be used in a current key change period to the DRM client;
a process in which the DRM client searches for a media decryption key corresponding to the key identifier received from the DASH decoder in the storage, and transmits the retrieved media decryption key to the DASH decoder; and
A process in which the DASH decoder uses the media decryption key received from the DRM client to decrypt the media segments received in the current key change period
A method for managing secure distribution of media content, further comprising: A method for managing secure distribution of media content in a system for a DASH-based media service, the method comprising:
A process in which the DASH encoder generates a plurality of media decryption keys and provides a key list including the generated media decryption keys to the content protection manager, wherein each media decryption key in the key list is identified by a Key Identifier (KID) identified;
transmitting, by the content protection manager, the key list received from the DASH encoder to a license server;
A process in which the license server generates a plurality of Entitlement Control Licenses (ECLs) based on the key list and transmits the ECL list including the generated ECLs to the content protection manager. In the ECL list, each ECL is identified by a key identifier. identified and containing an encrypted media decryption key and a key identifier;
generating, by the content protection manager, a pssh box in which the ECL list is inserted in a data field, and transmitting the generated pssh box to the DASH encoder; and
A process in which the DASH encoder includes the pssh box in a DASH MPD (Media Presentation Description) or media segment and delivers it to the client terminal
A method for managing the secure distribution of media content, including A computerized device operating as a content protection manager that manages the secure distribution of media content in a system for a DASH-based media service, comprising:
a memory storing computer program instructions;
one or more processors;
input/output interface circuit; and
one or more databuses interconnecting the memory, the processor, and the input/output interface circuitry;
The processor executes the computer program instructions to cause the computerized device,
transmitting a key list including media decryption keys from a DASH encoder to a license server, wherein each media decryption key in the key list is identified by a Key Identifier (KID);
receiving, from the license server, an ECL list generated based on the key list, wherein each ECL in the ECL list is identified by a key identifier and includes an encrypted media decryption key and a key identifier;
A process of creating a pssh box in which the ECL list is inserted in a data field, and transmitting the generated pssh box to the DASH encoder, where the pssh box is included in the DASH MPD or media segment by the DASH encoder and delivered to the client terminal ;
A computerized device that allows you to do A system for a DASH-based media service, comprising:
Connected to the client terminal through a content delivery network, comprising at least one server computer including a DASH encoder, a content protection manager, and a license server;
The DASH encoder generates a key list including a plurality of media decryption keys identified by a key identifier (KID), and includes a pssh box received from the license server in a DASH MPD (Media Presentation Description) or media segment. configured to deliver to the client terminal, wherein each media decryption key in the key list is identified by a Key Identifier (KID);
The license server is operable to generate a plurality of ECLs based on the key list, based on the key list, and deliver the ECL list including the generated ECLs to the content protection manager, wherein each ECL is a corresponding encrypted media contains a decryption key and a key identifier;
The content protection manager receives the key list from the DASH encoder and delivers it to the license server, generates a pssh box in which the ECL list received from the license server is inserted, and delivers the generated pssh box to the DASH encoder. Works, but here KID/ECL pairs are included in the Data field of pssh;
A system for a DASH-based media service, characterized in that.

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