Method and apparatus for playing back content based on digital rights management between portable storage and device, and portable storage for the same

A method of sending a right to play back content to a device from a portable storage, the method comprising:

• receiving a request to transmit the right to play back the content protected through digital rights management (DRM) from the device;
• transmitting the right to play back the content protected through DRM to the device in response to the request;
• and
• receiving a command to update a rights object for the content protected through DRM,
• wherein the right to play back content comprises permission information which is included in and obtained from the rights object, and
• wherein the command to update the rights object is a command to update at least one constraint included in the rights object stored in the portable storage by transmitting only a portion of the rights object, and not the entire rights object, to the portable storage.

A portable storage comprising:

• an interface module which connects to a device;
• a rights object storage module which stores at least one encrypted rights object;
• an encryption module which generates a session key and performs symmetric-key encryption and public-key encryption;
• and
• a digital rights management (DRM) agent module which performs DRM operations,
• wherein the DRM agent module finds a rights object for content among rights objects stored in the rights object storage module upon receiving a request to transmit a right to play back the content from the device through the interface module, encrypts information needed to play back the content among information comprised in the rights object using the encryption module, and sends the encrypted information to the device through the interface module,
• wherein the right to play back content comprises permission information which is included in and obtained from the rights object, and
• wherein the DRM agent module updates at least one constraint included in the rights object stored in the rights object storage module by receiving only a portion of the rights object, and not the entire rights object.

An apparatus for playing back content using a portable storage, the apparatus comprising:

• an interface module which connects to the portable storage;
• a content storage module which stores content protected through digital rights management (DRM);
• an encryption module which generates a session key and performs symmetric-key encryption and public-key encryption;
• and
• a DRM agent module which performs DRM operations,
• wherein the DRM agent module requests a right to play back the content that is protected through DRM and stored in the content storage module from the portable storage via the interface module, receives an encrypted right to play back the content from the portable storage, decrypts the encrypted right to play back the content using the encryption module, and obtains a content encryption key,
• wherein the right to play back content comprises permission information which is included in and obtained from a rights object, and
• wherein after a playback of the content is completed, the DRM agent requests the portable storage to update at least one constraint included in the rights object stored in the portable storage by transmitting only a portion of the rights object, and not the entire rights object, to the portable storage.

A recording medium having a computer readable program recorded therein, the program for executing a method of playing back content using a portable storage, the method comprising:

• requesting the portable storage to transmit a right to play back content protected through digital rights management (DRM);
• receiving the right to play back the content protected through DRM from the portable storage;
• and
• informing the portable storage of completion of a playback of the content protected through DRM using the right when the playback is completed,
• wherein the right to play back content comprises permission information which is included in and obtained from a rights object, and
• wherein the informing the portable storage of completion of a playback updates at least one constraint included in the rights object stored in the portable storage by transmitting only a portion of the rights object, and not the entire rights object, to the portable storage.

A recording medium having a computer readable program recorded therein, the program for executing a method of sending a right to play back content to a device from a portable storage, the method comprising:

• receiving a request to transmit the right to play back the content protected through digital rights management (DRM) from the device;
• transmitting the right to play back the content protected through DRM to the device in response to the request;
• and
• receiving a command to update a rights object for the content protected through DRM,
• wherein the right to play back content comprises permission information which is included in and obtained from the rights object, and
• wherein the command to update the rights object is a command to update at least one constraint included in the rights object stored in the portable storage by receiving only a portion of the rights object, and not the entire rights object.