Inter-entity coupling method, apparatus and system for content protection

Disclosed is an inter-entity coupling method for protecting content in a broadcast environment including a broadcast network and a terminal, the broadcast network having a Broadcast Service Application (BSA), a Broadcast Service Distribution (BSD), and a Broadcast Service Management (BSM), the inter-entity coupling method including performing, by the terminal, a registration process for obtaining a group key for the terminal; after the registration process is completed, performing, by the terminal, a service joining process for requesting service joining, and receiving, by the terminal, a Rights Object (RO) about the content from a message, which is received in response to the request, based on the obtained group key; obtaining a traffic key by using the RO, if a traffic key message is received after the service joining process is completed; receiving encrypted content in the terminal; and decrypting the encrypted content by using the traffic key.