Patent ID: 8386799

Claim:
A method of providing digital rights management (DRM) interoperability in a proxy agent with respect to a plurality of DRM service providers and a device which supports a predetermined DRM, comprising: at a first DRM service provider having keys EK 1 and EK 2 , a second DRM service provider having a key CEK A , the proxy agent, and the device, identifying each other; and proxy re-encrypting an interoperable content (IC) provided from the first DRM service provider and providing the IC to the device, wherein the IC comprises a key K M that is second-level encrypted using keys EK 1 and EK 2 of the first DRM service provider, wherein proxy re-encryption is performed by using a proxy key generated from proxy key information provided from the first DRM service provider and the second DRM service provider to provide DRM interoperability between different devices, wherein second-level encryption refers to an encryption technique which is performed in advance in order to perform the proxy re-encryption later, wherein proxy re-encrypting a second-level encrypted content generates a first-level encrypted content, and wherein proxy re-encrypting is expressed PRE PRoxYKEY (PRE2 EK1,EK2 (K M ))=PRE 1 CEKA (K M ).