Method and apparatus for generating rights object by reauthorization

Provided are a method and apparatus for generating a rights object (RO) by reauthorization. The method includes a second device mutually authenticating a first device, which received the first authorization information from a right issuer (RI), receiving a first RO from the first device, receiving a second authorization information from the first device, generating a third authorization information based on the second authorization information, changing the first RO to a second RO using the second authorization information, and transmitting the third authorization information and the second RO to an unauthorized device.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority from Korean Patent Application No. 10-2006-0084827, filed on Sep. 4, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatuses and methods consistent with the present invention relate to content use using digital rights management (DRM), and more particularly, to generating a rights object (RO) by reauthorization.

2. Description of the Related Art

In a related art DRM system, a content provider or a right issuer (RI) encrypts and then transmits content in order to control the use of content. Also, an RO, including a usage rule of the corresponding content, is issued in order to protect the rights of an author. Accordingly, a DRM device is designed to forcibly follow the usage rule included in the RO.

FIG. 1is a diagram illustrating the generation and distribution of an RO of related art content. Devices D1, D2, D3, and D4inside a domain each undergo a registration procedure by the corresponding service provider in order to register as a member in the domain. Accordingly, the devices D1, D2, D3, and D4can share content and an RO between other devices. Here, one representative device D1can share content and the RO from the other devices with the remaining devices D2, D3, and D4by transmitting the content and the RO. Then, the remaining devices D2, D3, and D4rely on the received content and the RO, using information from the service provider, and use the received content and the RO.

A method of sharing rights information, i.e., an RO, of the content using the domain is performed as shown inFIG. 1.

First, four devices are included in one domain and, in a domain technology based on a server, a content server includes a route certificate and a service provider certificate, for generating an encrypted content, a encryption key for using the encrypted content, and an RO including a usage rule. The route certificate is a certificate from a certificate issuer for checking an authorization system. The service provider certificate is a certificate in which a public key of the service provider is authorized by the certificate issuer.

Referring toFIG. 1, the devices D1, D2, and D3are registered with the RI and participate in the domain in operation S1. The device D1obtains content an RO from the RI in operation S2and transmits the obtained content and RO to the devices D2and D3in operation S3. Meanwhile, even when the device D1transmits the contents and RO to the device D4in operation S4, since the device D4has not yet been registered with the RI, a process of registering with the RI and joining the domain is required.

Processes of generating the RO of the encrypted content will now be described in detail. The service provider generates the encrypted content and RO using a content packaging process. The RO includes a content encryption key (CEK), which encrypts the content, and a usage rule. While generating the RO, important information, such as the CEK, or the like, is encrypted using a key of the device D1, which requested the content. Accordingly, a key for deciphering the content can be obtained only by the device D1using its own key, and thus, only the device D1can use the content.

Also, the RO is signed by a private key and the device D1confirms the signature of the RI using the route certificate owned by the device D1itself. If the signature of the RI is incorrect, the device D1is unable to use the corresponding RO.

Processes of using generated content and RO will now be described. In order for a device, which received the content and RO, to use the corresponding content, the device should check a signature of an RI on the received RO, decipher a rights encryption key (REK) of the RO, and decipher a CEK using the REK. Then, the content is deciphered using the CEK in order to use the content according to a usage rule owned by the RO.

As described above, in a re-distribution based on a server, the RO should be re-issued by the RI for the re-distribution.

Accordingly, when the content is re-distributed using a local domain manager, the following problems may occur. First, when the local domain manager changes a key included in the RO issued to itself, into a domain key in order to share the key with other devices inside the domain, the signature of the service provider is no longer effective. As a result, the service provider loses the authority to control the content changed by the local domain manager, and thus, unauthorized content can be distributed.

Second, the service provider is unable to determine a domain arbitrarily formed by the local domain manager, and is thus unable to determine in which domain content is used, which devices use the content, under what constraints is the content used, or the like.

Third, the devices (including a rendering device) in the domain should know a public key of the local domain manager in order to use the received content and RO, and should verify the validity of the certificate from the local domain manager every time. That is, when the local domain manager is hacked, unlimited re-distribution of the content may occur.

Moreover, in an Open Mobile Alliance (OMA) DRM environment, each device receives an RO, signed with a key of the RI, from the RI in order to be able to use the content. Accordingly, each device can authorize the received RO using the key of the RI that it owns itself. That is, all devices should have the key of the RI.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a mobile terminal for obtaining content required by a user, using a nearby terminal or a local server.

According to an aspect of the present invention, there is provided a method of generating an RO by reauthorization, the method including: a first device mutually authenticating a representative device, which received the first authorization information from an RI; receiving a first RO from the representative device; receiving a second authorization information from the representative device; generating a third authorization information based on the second authorization information; changing the first RO to a second RO using the second authorization information; and transmitting the third authorization information and the second RO to an unauthorized device.

The method may further include: a first device mutually authenticating the RI; receiving a third RO from the RI; receiving the first authorization information from the RI; and changing the third RO into the first RO using the first authorization information.

The representative device may be included in the same domain as the RI and the first device. The unauthorized device may not be included in the same domain as the first device.

The method may further include transmitting content, which can be used as the second RO, to the unauthorized device.

According to another aspect of the present invention, there is provided an apparatus for generating an RO by reauthorization, the apparatus including: a control unit which mutually authenticates a representative device, which received a first authorization information from an RI, and manages a first RO, received from the representative device; a reauthorization storage unit which stores a third authorization information generated based on a second authorization information received from the representative device; a rights object generation unit which changes the first RO to a second RO using the second authorization information; and a transceiver which transmits the third authorization information and the second RO to an unauthorized device.

According to another aspect of the present invention, there is provided an apparatus for generating an RO by reauthorization, the apparatus including: a control unit which mutually authenticates an RI and manages a first RO received from the RI; a reauthorization storage unit which stores a second authorization information generated based on a first authorization information received from the RI; a rights object generation unit which changes the first RO to a second RO using the first authorization information; and a transceiver which transmits the second authorization information and the second RO to the first device, wherein the first device is included in the same domain as the apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. In the drawings, like reference numerals denote like elements.

FIG. 2is a flowchart illustrating a process of generating a temporary RO according to an exemplary embodiment of the present invention.

In the current exemplary embodiment, an RI100is included in the same domain as a representative device200and a first device300, and a second device400is an external device, not included in the same domain.

Using the current exemplary embodiment as illustrated inFIG. 2, a certain user, having obtained predetermined content and an RO required for executing the predetermined content reproduces the rights object as a substitute RO, so that other devices can use the RO. In order to prevent an unauthorized reproduction of the substitute RO, the RI100may only allow a device, which is authorized with authorization information to generate a second RO. Accordingly, using the predetermined content is convenient and the predetermined content can be protected.

First, the RI100and the representative device200authenticate each other in operation S10. Then, after performing the authentication, the RI100generates authorization information in operation S20, and transmits the generated authorization information to the representative device200in operation S30. Here, the authorization information is information for verifying consent of the RI100when generating an RO.

Upon receiving the authorization information, the representative device200generates a second RO using the authorization information in operation S40, and transmits the generated second RO to the first device300in operation S50. The representative device200also generates reauthorization information, which reauthorizes the first device300to generate an RO, in operation S60, and transmits the generated reauthorization information to the first device300in operation S70.

The first device300uses the received second RO after authentication in operation S80, and generates a temporary RO using the received reauthorization information in operation S90. Then, the first device300transmits the generated temporary RO to the second device400in operation S100. Accordingly, the second device400uses the received temporary RO after authentication in operation S110.

The representative device200not only transmits the second RO to the first device300, but also transmits the reauthorization information, which enables the generation and transmission of the temporary RO, to the second device400, i.e., the external device. Accordingly, the second device400receives the temporary RO from the first device300, and does not directly receive the temporary RO from the representative device200.

FIG. 3is a diagram illustrating the generation of an RO according to an exemplary embodiment of the present invention. As shown inFIG. 3, the RI100authorizes the representative device200to generate the second RO, and a content provider150transmits content to the representative device200.

The representative device200reauthorizes the first device300, included in the same home domain, in order to generate a temporary RO, while transmitting the content to the first device300. The first device300generates the temporary RO and transmits the temporary RO to the second device400, which is not included in the home domain. In other words, upon receiving the content and reauthorization information from the representative device200, the first device300is moved to a domain outside the home domain by a user, and accordingly, the user transmits the content to the second device400through the first device300and resigns the temporary RO of the content using the reauthorization information. That is, the temporary RO is regenerated using the reauthorization information owned by the first device300, and is transmitted to the second device400.

FIG. 4is a block diagram illustrating the representative device200according to an exemplary embodiment of the present invention. As shown inFIG. 4, the representative device200includes a control unit210, an authorization storage unit220, a RO generation unit230, an encoder/decoder240, a reauthorization generation unit250, and a transceiver260. The control unit210performs an authentication on the RI100and manages the RO received from the RI100.

The authorization storage unit220stores a proxy certificate222, illustrated inFIG. 5, which is received from the RI100. That is, the representative device200generates pairs of new proxy public keys e and N and private keys d and N, which are different from its existing public key and private key, and stores the proxy certificate222, obtained from the RI100, in the authorization storage unit220.

FIG. 5is a diagram illustrating the proxy certificate222according to an exemplary embodiment of the present invention. As shown inFIG. 5, the proxy certificate222includes information about an issuer showing the RI, a serial number about the RO, subject about the RO, and key usage. The proxy certificate222also includes policy showing limits on downloading time, number of download times, etc., of the content, length constraint showing limits on number of reauthorization times, and proxy public keys e and N for generating the RO. When a value of the length constraint on a chain which can be reauthorized is 3, the representative device200can reauthorize two devices which are connected in the form of a chain. That is, the representative device200reauthorizes the first device300to generate the RO, and the first device300reauthorizes the second device400to generate the RO.

The RO generating unit230changes the RO into the newly signed second RO using the authorization information received from the RI100, so that other devices can use the RO, and stores the second RO.

The encoder/decoder240provides a function of encrypting the RO to the RO generating unit230.

When the RI100reauthorizes the representative device200, the reauthorization generation unit250generates authorization for generating the temporary RO inside the range of the given authorization, and transmits the authorization to the first device300. Accordingly, the representative device200generates a reauthorization key v, derived from its own proxy private key, and transmits the reauthorization key v to the first device300. That is, the representative device200generates the following reauthorization key v, using a warranty w about the reauthorization.
v=h(w,SN_first device)−dmodN[EQN. 1]

Also, the representative device200transmits the generated reauthorization key v, the warranty w, and the proxy certificate222to the first device300using the transceiver260.

The transceiver260exchanges information with the RI100or transmits the second RO to the first device300.

FIG. 6is a diagram illustrating the first device300according to an exemplary embodiment of the present invention. As shown inFIG. 6, the first device300includes a control unit310, a reauthorization storage unit320, a temporary RO generation unit330, an encoder/decoder340, and a transceiver360.

The control unit310performs authentication on the representative device200and manages the second RO received from the representative device200.

That is, by verifying the proxy certificate222received from the representative device200, the validity of public keys e and N of the representative device200is checked, and the validity of the reauthorization key v is verified as follows.
veh(w,SN_first device)=1modN[EQN. 2]

When the reauthorization key is determined to be valid, the reauthorization storage unit320stores the received reauthorization key v and the warranty w.

The temporary RO generation unit330generates the newly signed temporary RO, using the authorization information received from the representative device200, so that other devices can use the RO. Here, the temporary RO is an RO transmitted to a device outside the home domain, and has a small authorization range compared to the second RO.

That is, the first device300generates the temporary RO through the temporary RO generation unit330in order to share content with the second device400, which is an external device not included in the home domain.

The encoder/decoder340provides a function of encrypting the RO to the temporary RO generation unit330.

The transceiver350exchanges information with the representative device200or transmits the temporary RO to an unauthorized device (the second device400in the current exemplary embodiment).

FIG. 7is a diagram illustrating the temporary RO generated in the first device300according to an exemplary embodiment of the present invention.

As shown inFIG. 7, the temporary RO is formed of temporary right information Temp_Right and a reauthorization proxy signature Sign.

The temporary right information Temp_Right is license information signifying permission and constraint for using content, and includes a content identifier (ID), a serial number of a RO issuer, a content encryption key (CEK), and usage permission/constraint.

The reauthorization proxy signature Sign is a signature on the reauthorization about subordinate devices, which signs the temporary right information Temp_Right as the authorization information.

First, as shown inFIG. 7, the RO, generated in the first device300, is signed with a private key of the first device300and is transmitted to the second device400.

Upon receiving the RO, the second device400authorizes and uses the RO using its own public key.

At this time, the first device300prepares the temporary right information Temp-Right signifying a temporary usage permission, and signs the temporary right information Temp_Right with a reauthorization key, transmitted from the representative device200and stored in the reauthorization storage unit320. Here, a detailed algorithm is calculating k=h(Temp_Right, r), y=tvkmodN to ∀t ε[1,N], r=temodN.

At this time, an ID of an unauthorized device (the second device400in the current exemplary embodiment), receiving the temporary RO, may be added.

FIG. 8is a flowchart illustrating a process of registering a device and generating a temporary RO according to an exemplary embodiment of the present invention.

First, the RI100generates authorization information in operation S210. The authorization information is later transmitted to the representative device200so that the representative device200can generate a second RO. In order to generate the authorization information, a process of generating a random number and calculating a signature key is performed. After generating the authorization information, the representative device200is authenticated in operation S220. The representative device200is a device which can transmit the second RO to another device. The representative device200can be authenticated by using ID information of the representative device200.

After the authentication of the representative device200, the RI100, transmits an RO to the representative device200in operation S230. The transmitted RO may be an RO required for using content already stored in the representative device200, or an RO required for using content directly transmitted from the content provider150.

An example of the RO which is to be transmitted from the RI100to the representative device200in operation S230may include the following:
content ID∥E(REK, CEK)∥E(Device—prvkey, REK)∥Rights∥Sign(RI)∥Sign(RI, (R∥K))

Here, contentID is a content identifier, REK is an RO encryption key and CEK is a content encryption key. Device_prv key is a private key of the representative device200, and REK is encrypted using the private key. Also, Rights is the RO, Sign(RI) is a signature, and Sign(RI, R(∥K)) is a verification value on the signature.

As described above, the second RO is transmitted after an encryption using a private key generated during the authentication or a predetermined private key.

The RI100transmits the authorization information to the representative device200in operation S240. As described above, the authorization information includes signature information required for generating a new RO. Upon receiving the RO and the authorization information, the representative device200generates the second RO in operation S250. The second RO is generated using key information in the authorization information. At this time, usage rule information about an authorization signature key is provided together.

After generating reauthorization information using the same process as described above, the first device300is authenticated in operation S260. Also, the generated second RO is transmitted to the first device300in operation S270. The first device300can use the content using the second RO.

Here, an example of transmitting the second RO, after signing the second RO using the authorization signature, to the first device300includes the following:
content ID∥E(REK, CEK)∥E(Device 1—prvkey, REK)∥Rights∥Authorization Signature∥Authorization Signature Verification Value (R, K)∥Re-provider ID

Device1_prv key is a private key of the first device300, and the first device300receives the second RO by Authorization Signature. An Authorization Signature and Authorization Signature Verification Value are generated in operation S210, using authorization signature information transmitted in operation S240.

After operation S270, the first device300, upon receiving the second RO, determines validity of the authorization signature using a public key of the RI100.

When the representative device200re-provides the obtained second RO to the first device300, the authorization signature information and signed verification value information, included in the second RO which is to be re-provided, are required. Accordingly, the representative device200can only re-provide information permitted by the RI100.

The representative device200transmits the reauthorization information to the first device300in operation S280. As described above, the reauthorization information includes signature information required for generating a new RO. Upon receiving the RO and the reauthorization information, the first device300generates a temporary RO in operation S290. The temporary RO is generated using key information in the reauthorization information. At this time, usage rule information about a reauthorization signature key is provided together.

Then, the generated temporary RO is transmitted to a second device400, which is an external device, in operation S300. Accordingly, the second device400can use the content using the temporary RO.

An example of transmitting the temporary RO, after signing the temporary RO using the authorization signature, in operation S300includes the following:
content ID∥E(REK, CEK)∥E(Device 2—prvkey, REK)∥Rights∥Reauthorization Signature∥Reauthorization Signature Verification Value (R, K)∥Re-provider ID

Device2_prv key is a private key of the second device400, and the second device400receives the temporary RO by Reauthorization Signature. A Reauthorization Signature and Reauthorization Signature Verification Value are formed using the transmitted reauthorization information.

After operation S300, the second device400, upon receiving the temporary RO, determines validity of the authorization signature using the public key of the first device300.

When the first device300re-provides the obtained second RO to the second device400, the reauthorization signature information and signed verification value information, included in the temporary RO which is to be re-provided, are required. Accordingly, the first device300can only re-provide information permitted by the representative device200.

According to the current exemplary embodiment of the present invention, content bought by a user can be freely transmitted between various devices without violating a right of the content provider150, and without an intervention of the RI100and the representative device200.

That is, the representative device200receives the content from the content provider150and the RO on the content from the RI100.

Also, when the first device300, included in the same domain, requests to transmit the content, the representative device200transmits the content to the first device300, and at the same time, transmits the reauthorization information.

That is, when the second device400, not included in the same domain, requests a RO owned by the first device300, in order to use the content, the first device300performs operations which allows the second device400to use the RO.

Accordingly, the representative device200receives the authorization information from the RI100. The authorization information includes information which allows the representative device200to substitutively sign on the content directly. The representative device200signs the RO, signed with a key of the RI100, using the authorization information of the representative device200, and generates the second RO. Upon receiving the newly generated second RO, the first device300also receives the reauthorization information from the representative device200. The first device prepares the temporary RO and generates a signature using the reauthorization information. Also, the first device300transmits the temporary RO to the second device400, which is an external device.

At this time, since the second device400does not undergo processes of directly receiving a key from the RI100or the representative device200in order to use the temporary RO, an overhead caused by authentication can be reduced.

FIG. 9is a diagram illustrating the generation of an RO according to another exemplary embodiment of the present invention. The rights issuer100and the representative device200perform authentication mutually. After the authentication, the representative device200receives the RO and the authorization information from the RI100. Then, the first device300, included in the same domain as the representative device200, receives the second RO from the representative device200by means of the authentication from the representative device200, and receives the reauthorization information. Similarly, the second device400, included in the same domain as the first device300, receives a third RO from the first device300by means of the authentication from the first device300, and receives the reauthorization information. Next, a third device500, not included in the same domain as the second device400, receives the temporary RO from the second device400by means of the authentication from the second device400, and receives the reauthorization information.

As shown inFIG. 9, the third device500, which is not included in the same domain, does not directly receive the temporary RO from the representative device200, but can receive the temporary RO from the second device400, which receives the reauthorization information by means of the representative device200and the first device300.

Accordingly, consent of the RI100can be confirmed without an interaction between the RI100and the representative device200, and thus content can be used without damaging profits of the content provider150.

At this time, a device (not shown), included in the same domain as the second device400, can be connected between the second device400and the third device500in the form of a chain in order to transmit the RO from the RI100to the third device500.

The method of generating the RO by reauthorization according to the exemplary embodiment of the present invention can be written as a computer program. Codes and code segments for accomplishing the exemplary embodiment of the present invention can be easily construed by programmers of ordinary skill in the art to which the present invention pertains. The computer program is stored in computer readable medium, and the method of generating the RO by reauthorization can be embodied by reading and executing the computer readable medium in a computer. Examples of the computer readable medium include magnetic recording medium, optical recording medium, and carrier wave medium.

According to the exemplary embodiment of the present invention, by reauthorizing a RI with a right to generate an RO between devices connected in the form of a chain, content can be shared by a device not included in the same domain as the right issuer. Accordingly, the content can be shared without an intervention of the RI or a representative device, and can be used without damaging profits of a content provider.